From 59029aec30ff6b3cb2d9c74af77fe96a5f108595 Mon Sep 17 00:00:00 2001
From: Matthias Sohn <matthias.sohn@sap.com>
Date: Fri, 11 Nov 2022 17:54:06 +0100
Subject: [PATCH] Add option to allow using JDK's SHA1 implementation

The change If6da9833 moved the computation of SHA1 from the JVM's
JCE to a pure Java implementation with collision detection.
The extra security for public sites comes with a cost of slower
SHA1 processing compared to the native implementation in the JDK.

When JGit is used internally and not exposed to any traffic from
external or untrusted users, the extra cost of the pure Java SHA1
implementation can be avoided, falling back to the previous
native MessageDigest implementation.

Bug: 580310
Change-Id: Ic24c0ba1cb0fb6282b8ca3025ffbffa84035565e
---
 .../org/eclipse/jgit/util/sha1/SHA1Test.java  |  69 ++-
 .../org/eclipse/jgit/lib/ConfigConstants.java |   7 +
 .../src/org/eclipse/jgit/util/sha1/SHA1.java  | 584 +++---------------
 .../org/eclipse/jgit/util/sha1/SHA1Java.java  | 579 +++++++++++++++++
 .../eclipse/jgit/util/sha1/SHA1Native.java    |  75 +++
 .../util/sha1/Sha1CollisionException.java     |   2 +-
 6 files changed, 823 insertions(+), 493 deletions(-)
 create mode 100644 org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Java.java
 create mode 100644 org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Native.java

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/sha1/SHA1Test.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/sha1/SHA1Test.java
index ad560c2546..abc2854faf 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/sha1/SHA1Test.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/util/sha1/SHA1Test.java
@@ -14,6 +14,7 @@ import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
+import static org.junit.Assume.assumeFalse;
 import static org.junit.Assume.assumeTrue;
 
 import java.io.IOException;
@@ -22,11 +23,20 @@ import java.nio.ByteBuffer;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 
+import org.eclipse.jgit.junit.MockSystemReader;
 import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.util.IO;
-import org.junit.Test;
-
+import org.eclipse.jgit.util.SystemReader;
+import org.eclipse.jgit.util.sha1.SHA1.Sha1Implementation;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.experimental.theories.DataPoints;
+import org.junit.experimental.theories.Theories;
+import org.junit.experimental.theories.Theory;
+import org.junit.runner.RunWith;
+
+@RunWith(Theories.class)
 public class SHA1Test {
 	private static final String TEST1 = "abc";
 
@@ -34,7 +44,32 @@ public class SHA1Test {
 	private static final String TEST2b = "jkijkljklmklmnlmnomnopnopq";
 	private static final String TEST2 = TEST2a + TEST2b;
 
-	@Test
+	@DataPoints
+	public static Sha1Implementation[] getDataPoints() {
+		return new Sha1Implementation[] { Sha1Implementation.JAVA,
+				Sha1Implementation.JDKNATIVE };
+	}
+
+	private Sha1Implementation sha1Implementation;
+
+	public SHA1Test(Sha1Implementation impl) {
+		this.sha1Implementation = impl;
+	}
+
+	@Before
+	public void setUp() throws Exception {
+		MockSystemReader mockSystemReader = new MockSystemReader();
+		SystemReader.setInstance(mockSystemReader);
+			System.setProperty("org.eclipse.jgit.util.sha1.implementation",
+					sha1Implementation.name());
+	}
+
+	@After
+	public void tearDown() {
+		SystemReader.setInstance(null);
+	}
+
+	@Theory
 	public void test0() throws NoSuchAlgorithmException {
 		ObjectId exp = ObjectId
 				.fromString("da39a3ee5e6b4b0d3255bfef95601890afd80709");
@@ -56,7 +91,7 @@ public class SHA1Test {
 		assertEquals(exp, s2);
 	}
 
-	@Test
+	@Theory
 	public void test1() throws NoSuchAlgorithmException {
 		ObjectId exp = ObjectId
 				.fromString("a9993e364706816aba3e25717850c26c9cd0d89d");
@@ -78,7 +113,7 @@ public class SHA1Test {
 		assertEquals(exp, s2);
 	}
 
-	@Test
+	@Theory
 	public void test2() throws NoSuchAlgorithmException {
 		ObjectId exp = ObjectId
 				.fromString("84983e441c3bd26ebaae4aa1f95129e5e54670f1");
@@ -100,9 +135,13 @@ public class SHA1Test {
 		assertEquals(exp, s2);
 	}
 
-	@Test
+	@Theory
 	public void shatteredCollision()
 			throws IOException, NoSuchAlgorithmException {
+		assumeFalse(
+				System.getProperty("org.eclipse.jgit.util.sha1.implementation")
+						.equalsIgnoreCase("jdkNative"));
+
 		byte[] pdf1 = read("shattered-1.pdf", 422435);
 		byte[] pdf2 = read("shattered-2.pdf", 422435);
 		MessageDigest md;
@@ -149,8 +188,12 @@ public class SHA1Test {
 		}
 	}
 
-	@Test
+	@Theory
 	public void shatteredStoredInGitBlob() throws IOException {
+		assumeFalse(
+				System.getProperty("org.eclipse.jgit.util.sha1.implementation")
+						.equalsIgnoreCase("jdkNative"));
+
 		byte[] pdf1 = read("shattered-1.pdf", 422435);
 		byte[] pdf2 = read("shattered-2.pdf", 422435);
 
@@ -158,8 +201,10 @@ public class SHA1Test {
 		// the Git blob header permutes the data enough for this specific
 		// attack example to not be detected as a collision. (A different file
 		// pair that takes the Git header into account however, would.)
-		ObjectId id1 = blob(pdf1, SHA1.newInstance().setDetectCollision(true));
-		ObjectId id2 = blob(pdf2, SHA1.newInstance().setDetectCollision(true));
+		ObjectId id1 = blob(pdf1,
+				SHA1.newInstance().setDetectCollision(true));
+		ObjectId id2 = blob(pdf2,
+				SHA1.newInstance().setDetectCollision(true));
 
 		assertEquals(
 				ObjectId.fromString("ba9aaa145ccd24ef760cf31c74d8f7ca1a2e47b0"),
@@ -169,8 +214,12 @@ public class SHA1Test {
 				id2);
 	}
 
-	@Test
+	@Theory
 	public void detectsShatteredByDefault() throws IOException {
+		assumeFalse(
+				System.getProperty("org.eclipse.jgit.util.sha1.implementation")
+						.equalsIgnoreCase("jdkNative"));
+
 		assumeTrue(System.getProperty("org.eclipse.jgit.util.sha1.detectCollision") == null);
 		assumeTrue(System.getProperty("org.eclipse.jgit.util.sha1.safeHash") == null);
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 24eebc6a19..924328d8a6 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@ -437,6 +437,13 @@ public final class ConfigConstants {
 	 */
 	public static final String CONFIG_KEY_SUPPORTSATOMICFILECREATION = "supportsatomicfilecreation";
 
+	/**
+	 * The "sha1Implementation" key in the "core" section
+	 *
+	 * @since 5.13.2
+	 */
+	public static final String SHA1_IMPLEMENTATION = "sha1implementation";
+
 	/**
 	 * The "noprefix" key in the "diff" section
 	 * @since 3.0
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1.java
index 1420add662..87993d2bee 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2017, Google Inc. and others
+ * Copyright (C) 2022, Matthias Sohn <matthias.sohn@sap.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -7,99 +7,96 @@
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
-
 package org.eclipse.jgit.util.sha1;
 
-import static java.lang.Integer.lowestOneBit;
-import static java.lang.Integer.numberOfTrailingZeros;
-import static java.lang.Integer.rotateLeft;
-import static java.lang.Integer.rotateRight;
-
-import java.text.MessageFormat;
-import java.util.Arrays;
+import java.io.IOException;
+import java.security.MessageDigest;
 
-import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.MutableObjectId;
 import org.eclipse.jgit.lib.ObjectId;
-import org.eclipse.jgit.util.NB;
 import org.eclipse.jgit.util.SystemReader;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
- * Pure Java implementation of SHA-1 from FIPS 180-1 / RFC 3174.
- *
+ * SHA-1 interface from FIPS 180-1 / RFC 3174 with optional collision detection.
+ * Some implementations may not support collision detection.
  * <p>
  * See <a href="https://tools.ietf.org/html/rfc3174">RFC 3174</a>.
- * <p>
- * Unlike MessageDigest, this implementation includes the algorithm used by
- * {@code sha1dc} to detect cryptanalytic collision attacks against SHA-1, such
- * as the one used by <a href="https://shattered.it/">SHAttered</a>. See
- * <a href="https://github.com/cr-marcstevens/sha1collisiondetection">
- * sha1collisiondetection</a> for more information.
- * <p>
- * When detectCollision is true (default), this implementation throws
- * {@link org.eclipse.jgit.util.sha1.Sha1CollisionException} from any digest
- * method if a potential collision was detected.
- *
- * @since 4.7
  */
-public class SHA1 {
-	private static final Logger LOG = LoggerFactory.getLogger(SHA1.class);
-	private static final boolean DETECT_COLLISIONS;
-
-	static {
-		SystemReader sr = SystemReader.getInstance();
-		String v = sr.getProperty("org.eclipse.jgit.util.sha1.detectCollision"); //$NON-NLS-1$
-		DETECT_COLLISIONS = v != null ? Boolean.parseBoolean(v) : true;
-	}
-
+public abstract class SHA1 {
 	/**
-	 * Create a new context to compute a SHA-1 hash of data.
-	 *
-	 * @return a new context to compute a SHA-1 hash of data.
+	 * SHA1 implementations available in JGit
 	 */
-	public static SHA1 newInstance() {
-		return new SHA1();
-	}
-
-	private final State h = new State();
-	private final int[] w = new int[80];
-
-	/** Buffer to accumulate partial blocks to 64 byte alignment. */
-	private final byte[] buffer = new byte[64];
+	public enum Sha1Implementation {
+		/**
+		 * {@link SHA1Java} implemented in Java, supports collision detection.
+		 */
+		JAVA(SHA1Java.class),
+		/**
+		 * Native implementation based on JDK's {@link MessageDigest}.
+		 */
+		JDKNATIVE(SHA1Native.class);
+
+		private final String implClassName;
+
+		private Sha1Implementation(Class implClass) {
+			this.implClassName = implClass.getName();
+		}
 
-	/** Total number of bytes in the message. */
-	private long length;
+		@Override
+		public String toString() {
+			return implClassName;
+		}
+	}
 
-	private boolean detectCollision = DETECT_COLLISIONS;
-	private boolean foundCollision;
+	private static final Sha1Implementation SHA1_IMPLEMENTATION = fromConfig();
 
-	private final int[] w2 = new int[80];
-	private final State state58 = new State();
-	private final State state65 = new State();
-	private final State hIn = new State();
-	private final State hTmp = new State();
+	private static Sha1Implementation fromConfig() {
+		try {
+			return SystemReader.getInstance().getUserConfig().getEnum(
+					ConfigConstants.CONFIG_CORE_SECTION, null,
+					ConfigConstants.SHA1_IMPLEMENTATION,
+					Sha1Implementation.JAVA);
+		} catch (ConfigInvalidException | IOException e) {
+			return Sha1Implementation.JAVA;
+		}
+	}
 
-	private SHA1() {
-		h.init();
+	private static Sha1Implementation getImplementation() {
+		String fromSystemProperty = System
+				.getProperty("org.eclipse.jgit.util.sha1.implementation"); //$NON-NLS-1$
+		if (fromSystemProperty == null) {
+			return SHA1_IMPLEMENTATION;
+		}
+		if (fromSystemProperty
+				.equalsIgnoreCase(Sha1Implementation.JAVA.name())) {
+			return Sha1Implementation.JAVA;
+		}
+		if (fromSystemProperty
+				.equalsIgnoreCase(Sha1Implementation.JDKNATIVE.name())) {
+			return Sha1Implementation.JDKNATIVE;
+		}
+		return SHA1_IMPLEMENTATION;
 	}
 
 	/**
-	 * Enable likely collision detection.
-	 * <p>
-	 * Default is {@code true}.
+	 * Create a new context to compute a SHA-1 hash of data.
 	 * <p>
-	 * May also be set by system property:
-	 * {@code -Dorg.eclipse.jgit.util.sha1.detectCollision=true}.
+	 * If {@code core.sha1Implementation = jdkNative} in the user level global
+	 * git configuration or the system property
+	 * {@code org.eclipse.jgit.util.sha1.implementation = jdkNative} it will
+	 * create an object using the implementation in the JDK. If both are set the
+	 * system property takes precedence. Otherwise the pure Java implementation
+	 * will be used which supports collision detection but is slower.
 	 *
-	 * @param detect
-	 *            a boolean.
-	 * @return {@code this}
+	 * @return a new context to compute a SHA-1 hash of data.
 	 */
-	public SHA1 setDetectCollision(boolean detect) {
-		detectCollision = detect;
-		return this;
+	public static SHA1 newInstance() {
+		if (getImplementation() == Sha1Implementation.JDKNATIVE) {
+			return new SHA1Native();
+		}
+		return new SHA1Java();
 	}
 
 	/**
@@ -107,14 +104,7 @@ public class SHA1 {
 	 *
 	 * @param b a byte.
 	 */
-	public void update(byte b) {
-		int bufferLen = (int) (length & 63);
-		length++;
-		buffer[bufferLen] = b;
-		if (bufferLen == 63) {
-			compress(buffer, 0);
-		}
-	}
+	public abstract void update(byte b);
 
 	/**
 	 * Update the digest computation by adding bytes to the message.
@@ -122,9 +112,7 @@ public class SHA1 {
 	 * @param in
 	 *            input array of bytes.
 	 */
-	public void update(byte[] in) {
-		update(in, 0, in.length);
-	}
+	public abstract void update(byte[] in);
 
 	/**
 	 * Update the digest computation by adding bytes to the message.
@@ -136,344 +124,7 @@ public class SHA1 {
 	 * @param len
 	 *            number of bytes to hash.
 	 */
-	public void update(byte[] in, int p, int len) {
-		// SHA-1 compress can only process whole 64 byte blocks.
-		// Hold partial updates in buffer, whose length is the low bits.
-		int bufferLen = (int) (length & 63);
-		length += len;
-
-		if (bufferLen > 0) {
-			int n = Math.min(64 - bufferLen, len);
-			System.arraycopy(in, p, buffer, bufferLen, n);
-			p += n;
-			len -= n;
-			if (bufferLen + n < 64) {
-				return;
-			}
-			compress(buffer, 0);
-		}
-		while (len >= 64) {
-			compress(in, p);
-			p += 64;
-			len -= 64;
-		}
-		if (len > 0) {
-			System.arraycopy(in, p, buffer, 0, len);
-		}
-	}
-
-	private void compress(byte[] block, int p) {
-		initBlock(block, p);
-		int ubcDvMask = detectCollision ? UbcCheck.check(w) : 0;
-		compress();
-
-		while (ubcDvMask != 0) {
-			int b = numberOfTrailingZeros(lowestOneBit(ubcDvMask));
-			UbcCheck.DvInfo dv = UbcCheck.DV[b];
-			for (int i = 0; i < 80; i++) {
-				w2[i] = w[i] ^ dv.dm[i];
-			}
-			recompress(dv.testt);
-			if (eq(hTmp, h)) {
-				foundCollision = true;
-				break;
-			}
-			ubcDvMask &= ~(1 << b);
-		}
-	}
-
-	private void initBlock(byte[] block, int p) {
-		for (int t = 0; t < 16; t++) {
-			w[t] = NB.decodeInt32(block, p + (t << 2));
-		}
-
-		// RFC 3174 6.1.b, extend state vector to 80 words.
-		for (int t = 16; t < 80; t++) {
-			int x = w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16];
-			w[t] = rotateLeft(x, 1); // S^1(...)
-		}
-	}
-
-	private void compress() {
-		// Method 1 from RFC 3174 section 6.1.
-		// Method 2 (circular queue of 16 words) is slower.
-		int a = h.a, b = h.b, c = h.c, d = h.d, e = h.e;
-
-		// @formatter:off
-		 e += s1(a, b, c, d,w[ 0]);  b = rotateLeft( b, 30);
-		 d += s1(e, a, b, c,w[ 1]);  a = rotateLeft( a, 30);
-		 c += s1(d, e, a, b,w[ 2]);  e = rotateLeft( e, 30);
-		 b += s1(c, d, e, a,w[ 3]);  d = rotateLeft( d, 30);
-		 a += s1(b, c, d, e,w[ 4]);  c = rotateLeft( c, 30);
-		 e += s1(a, b, c, d,w[ 5]);  b = rotateLeft( b, 30);
-		 d += s1(e, a, b, c,w[ 6]);  a = rotateLeft( a, 30);
-		 c += s1(d, e, a, b,w[ 7]);  e = rotateLeft( e, 30);
-		 b += s1(c, d, e, a,w[ 8]);  d = rotateLeft( d, 30);
-		 a += s1(b, c, d, e,w[ 9]);  c = rotateLeft( c, 30);
-		 e += s1(a, b, c, d,w[ 10]);  b = rotateLeft( b, 30);
-		 d += s1(e, a, b, c,w[ 11]);  a = rotateLeft( a, 30);
-		 c += s1(d, e, a, b,w[ 12]);  e = rotateLeft( e, 30);
-		 b += s1(c, d, e, a,w[ 13]);  d = rotateLeft( d, 30);
-		 a += s1(b, c, d, e,w[ 14]);  c = rotateLeft( c, 30);
-		 e += s1(a, b, c, d,w[ 15]);  b = rotateLeft( b, 30);
-		 d += s1(e, a, b, c,w[ 16]);  a = rotateLeft( a, 30);
-		 c += s1(d, e, a, b,w[ 17]);  e = rotateLeft( e, 30);
-		 b += s1(c, d, e, a,w[ 18]);  d = rotateLeft( d, 30);
-		 a += s1(b, c, d, e,w[ 19]);  c = rotateLeft( c, 30);
-
-		 e += s2(a, b, c, d,w[ 20]);  b = rotateLeft( b, 30);
-		 d += s2(e, a, b, c,w[ 21]);  a = rotateLeft( a, 30);
-		 c += s2(d, e, a, b,w[ 22]);  e = rotateLeft( e, 30);
-		 b += s2(c, d, e, a,w[ 23]);  d = rotateLeft( d, 30);
-		 a += s2(b, c, d, e,w[ 24]);  c = rotateLeft( c, 30);
-		 e += s2(a, b, c, d,w[ 25]);  b = rotateLeft( b, 30);
-		 d += s2(e, a, b, c,w[ 26]);  a = rotateLeft( a, 30);
-		 c += s2(d, e, a, b,w[ 27]);  e = rotateLeft( e, 30);
-		 b += s2(c, d, e, a,w[ 28]);  d = rotateLeft( d, 30);
-		 a += s2(b, c, d, e,w[ 29]);  c = rotateLeft( c, 30);
-		 e += s2(a, b, c, d,w[ 30]);  b = rotateLeft( b, 30);
-		 d += s2(e, a, b, c,w[ 31]);  a = rotateLeft( a, 30);
-		 c += s2(d, e, a, b,w[ 32]);  e = rotateLeft( e, 30);
-		 b += s2(c, d, e, a,w[ 33]);  d = rotateLeft( d, 30);
-		 a += s2(b, c, d, e,w[ 34]);  c = rotateLeft( c, 30);
-		 e += s2(a, b, c, d,w[ 35]);  b = rotateLeft( b, 30);
-		 d += s2(e, a, b, c,w[ 36]);  a = rotateLeft( a, 30);
-		 c += s2(d, e, a, b,w[ 37]);  e = rotateLeft( e, 30);
-		 b += s2(c, d, e, a,w[ 38]);  d = rotateLeft( d, 30);
-		 a += s2(b, c, d, e,w[ 39]);  c = rotateLeft( c, 30);
-
-		 e += s3(a, b, c, d,w[ 40]);  b = rotateLeft( b, 30);
-		 d += s3(e, a, b, c,w[ 41]);  a = rotateLeft( a, 30);
-		 c += s3(d, e, a, b,w[ 42]);  e = rotateLeft( e, 30);
-		 b += s3(c, d, e, a,w[ 43]);  d = rotateLeft( d, 30);
-		 a += s3(b, c, d, e,w[ 44]);  c = rotateLeft( c, 30);
-		 e += s3(a, b, c, d,w[ 45]);  b = rotateLeft( b, 30);
-		 d += s3(e, a, b, c,w[ 46]);  a = rotateLeft( a, 30);
-		 c += s3(d, e, a, b,w[ 47]);  e = rotateLeft( e, 30);
-		 b += s3(c, d, e, a,w[ 48]);  d = rotateLeft( d, 30);
-		 a += s3(b, c, d, e,w[ 49]);  c = rotateLeft( c, 30);
-		 e += s3(a, b, c, d,w[ 50]);  b = rotateLeft( b, 30);
-		 d += s3(e, a, b, c,w[ 51]);  a = rotateLeft( a, 30);
-		 c += s3(d, e, a, b,w[ 52]);  e = rotateLeft( e, 30);
-		 b += s3(c, d, e, a,w[ 53]);  d = rotateLeft( d, 30);
-		 a += s3(b, c, d, e,w[ 54]);  c = rotateLeft( c, 30);
-		 e += s3(a, b, c, d,w[ 55]);  b = rotateLeft( b, 30);
-		 d += s3(e, a, b, c,w[ 56]);  a = rotateLeft( a, 30);
-		 c += s3(d, e, a, b,w[ 57]);  e = rotateLeft( e, 30);
-		state58.save(a, b, c, d, e);
-		 b += s3(c, d, e, a,w[ 58]);  d = rotateLeft( d, 30);
-		 a += s3(b, c, d, e,w[ 59]);  c = rotateLeft( c, 30);
-
-		 e += s4(a, b, c, d,w[ 60]);  b = rotateLeft( b, 30);
-		 d += s4(e, a, b, c,w[ 61]);  a = rotateLeft( a, 30);
-		 c += s4(d, e, a, b,w[ 62]);  e = rotateLeft( e, 30);
-		 b += s4(c, d, e, a,w[ 63]);  d = rotateLeft( d, 30);
-		 a += s4(b, c, d, e,w[ 64]);  c = rotateLeft( c, 30);
-		state65.save(a, b, c, d, e);
-		 e += s4(a, b, c, d,w[ 65]);  b = rotateLeft( b, 30);
-		 d += s4(e, a, b, c,w[ 66]);  a = rotateLeft( a, 30);
-		 c += s4(d, e, a, b,w[ 67]);  e = rotateLeft( e, 30);
-		 b += s4(c, d, e, a,w[ 68]);  d = rotateLeft( d, 30);
-		 a += s4(b, c, d, e,w[ 69]);  c = rotateLeft( c, 30);
-		 e += s4(a, b, c, d,w[ 70]);  b = rotateLeft( b, 30);
-		 d += s4(e, a, b, c,w[ 71]);  a = rotateLeft( a, 30);
-		 c += s4(d, e, a, b,w[ 72]);  e = rotateLeft( e, 30);
-		 b += s4(c, d, e, a,w[ 73]);  d = rotateLeft( d, 30);
-		 a += s4(b, c, d, e,w[ 74]);  c = rotateLeft( c, 30);
-		 e += s4(a, b, c, d,w[ 75]);  b = rotateLeft( b, 30);
-		 d += s4(e, a, b, c,w[ 76]);  a = rotateLeft( a, 30);
-		 c += s4(d, e, a, b,w[ 77]);  e = rotateLeft( e, 30);
-		 b += s4(c, d, e, a,w[ 78]);  d = rotateLeft( d, 30);
-		 a += s4(b, c, d, e,w[ 79]);  c = rotateLeft( c, 30);
-
-		// @formatter:on
-		h.save(h.a + a, h.b + b, h.c + c, h.d + d, h.e + e);
-	}
-
-	private void recompress(int t) {
-		State s;
-		switch (t) {
-		case 58:
-			s = state58;
-			break;
-		case 65:
-			s = state65;
-			break;
-		default:
-			throw new IllegalStateException();
-		}
-		int a = s.a, b = s.b, c = s.c, d = s.d, e = s.e;
-
-		// @formatter:off
-	  if (t == 65) {
-		{ c = rotateRight( c, 30);  a -= s4(b, c, d, e,w2[ 64]);}
-		{ d = rotateRight( d, 30);  b -= s4(c, d, e, a,w2[ 63]);}
-		{ e = rotateRight( e, 30);  c -= s4(d, e, a, b,w2[ 62]);}
-		{ a = rotateRight( a, 30);  d -= s4(e, a, b, c,w2[ 61]);}
-		{ b = rotateRight( b, 30);  e -= s4(a, b, c, d,w2[ 60]);}
-
-		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 59]);}
-		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 58]);}
-	  }
-		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 57]);}
-		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 56]);}
-		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 55]);}
-		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 54]);}
-		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 53]);}
-		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 52]);}
-		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 51]);}
-		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 50]);}
-		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 49]);}
-		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 48]);}
-		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 47]);}
-		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 46]);}
-		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 45]);}
-		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 44]);}
-		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 43]);}
-		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 42]);}
-		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 41]);}
-		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 40]);}
-
-		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 39]);}
-		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 38]);}
-		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 37]);}
-		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 36]);}
-		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 35]);}
-		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 34]);}
-		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 33]);}
-		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 32]);}
-		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 31]);}
-		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 30]);}
-		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 29]);}
-		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 28]);}
-		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 27]);}
-		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 26]);}
-		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 25]);}
-		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 24]);}
-		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 23]);}
-		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 22]);}
-		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 21]);}
-		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 20]);}
-
-		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 19]);}
-		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 18]);}
-		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 17]);}
-		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 16]);}
-		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 15]);}
-		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 14]);}
-		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 13]);}
-		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 12]);}
-		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 11]);}
-		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 10]);}
-		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 9]);}
-		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 8]);}
-		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 7]);}
-		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 6]);}
-		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 5]);}
-		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 4]);}
-		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 3]);}
-		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 2]);}
-		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 1]);}
-		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 0]);}
-
-		hIn.save(a, b, c, d, e);
-		a = s.a; b = s.b; c = s.c; d = s.d; e = s.e;
-
-	  if (t == 58) {
-		{ b += s3(c, d, e, a,w2[ 58]);  d = rotateLeft( d, 30);}
-		{ a += s3(b, c, d, e,w2[ 59]);  c = rotateLeft( c, 30);}
-
-		{ e += s4(a, b, c, d,w2[ 60]);  b = rotateLeft( b, 30);}
-		{ d += s4(e, a, b, c,w2[ 61]);  a = rotateLeft( a, 30);}
-		{ c += s4(d, e, a, b,w2[ 62]);  e = rotateLeft( e, 30);}
-		{ b += s4(c, d, e, a,w2[ 63]);  d = rotateLeft( d, 30);}
-		{ a += s4(b, c, d, e,w2[ 64]);  c = rotateLeft( c, 30);}
-	  }
-		{ e += s4(a, b, c, d,w2[ 65]);  b = rotateLeft( b, 30);}
-		{ d += s4(e, a, b, c,w2[ 66]);  a = rotateLeft( a, 30);}
-		{ c += s4(d, e, a, b,w2[ 67]);  e = rotateLeft( e, 30);}
-		{ b += s4(c, d, e, a,w2[ 68]);  d = rotateLeft( d, 30);}
-		{ a += s4(b, c, d, e,w2[ 69]);  c = rotateLeft( c, 30);}
-		{ e += s4(a, b, c, d,w2[ 70]);  b = rotateLeft( b, 30);}
-		{ d += s4(e, a, b, c,w2[ 71]);  a = rotateLeft( a, 30);}
-		{ c += s4(d, e, a, b,w2[ 72]);  e = rotateLeft( e, 30);}
-		{ b += s4(c, d, e, a,w2[ 73]);  d = rotateLeft( d, 30);}
-		{ a += s4(b, c, d, e,w2[ 74]);  c = rotateLeft( c, 30);}
-		{ e += s4(a, b, c, d,w2[ 75]);  b = rotateLeft( b, 30);}
-		{ d += s4(e, a, b, c,w2[ 76]);  a = rotateLeft( a, 30);}
-		{ c += s4(d, e, a, b,w2[ 77]);  e = rotateLeft( e, 30);}
-		{ b += s4(c, d, e, a,w2[ 78]);  d = rotateLeft( d, 30);}
-		{ a += s4(b, c, d, e,w2[ 79]);  c = rotateLeft( c, 30);}
-
-		// @formatter:on
-		hTmp.save(hIn.a + a, hIn.b + b, hIn.c + c, hIn.d + d, hIn.e + e);
-	}
-
-	private static int s1(int a, int b, int c, int d, int w_t) {
-		return rotateLeft(a, 5)
-				// f: 0 <= t <= 19
-				+ ((b & c) | ((~b) & d))
-				+ 0x5A827999 + w_t;
-	}
-
-	private static int s2(int a, int b, int c, int d, int w_t) {
-		return rotateLeft(a, 5)
-				// f: 20 <= t <= 39
-				+ (b ^ c ^ d)
-				+ 0x6ED9EBA1 + w_t;
-	}
-
-	private static int s3(int a, int b, int c, int d, int w_t) {
-		return rotateLeft(a, 5)
-				// f: 40 <= t <= 59
-				+ ((b & c) | (b & d) | (c & d))
-				+ 0x8F1BBCDC + w_t;
-	}
-
-	private static int s4(int a, int b, int c, int d, int w_t) {
-		return rotateLeft(a, 5)
-				// f: 60 <= t <= 79
-				+ (b ^ c ^ d)
-				+ 0xCA62C1D6 + w_t;
-	}
-
-	private static boolean eq(State q, State r) {
-		return q.a == r.a
-				&& q.b == r.b
-				&& q.c == r.c
-				&& q.d == r.d
-				&& q.e == r.e;
-	}
-
-	private void finish() {
-		int bufferLen = (int) (length & 63);
-		if (bufferLen > 55) {
-			// Last block is too small; pad, compress, pad another block.
-			buffer[bufferLen++] = (byte) 0x80;
-			Arrays.fill(buffer, bufferLen, 64, (byte) 0);
-			compress(buffer, 0);
-			Arrays.fill(buffer, 0, 56, (byte) 0);
-		} else {
-			// Last block can hold padding and length.
-			buffer[bufferLen++] = (byte) 0x80;
-			Arrays.fill(buffer, bufferLen, 56, (byte) 0);
-		}
-
-		// SHA-1 appends the length of the message in bits after the
-		// padding block (above). Here length is in bytes. Multiply by
-		// 8 by shifting by 3 as part of storing the 64 bit byte length
-		// into the two words expected in the trailer.
-		NB.encodeInt32(buffer, 56, (int) (length >>> (32 - 3)));
-		NB.encodeInt32(buffer, 60, (int) (length << 3));
-		compress(buffer, 0);
-
-		if (foundCollision) {
-			ObjectId id = h.toObjectId();
-			LOG.warn(MessageFormat.format(JGitText.get().sha1CollisionDetected,
-					id.name()));
-			throw new Sha1CollisionException(id);
-		}
-	}
+	public abstract void update(byte[] in, int p, int len);
 
 	/**
 	 * Finish the digest and return the resulting hash.
@@ -484,17 +135,7 @@ public class SHA1 {
 	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
-	public byte[] digest() throws Sha1CollisionException {
-		finish();
-
-		byte[] b = new byte[20];
-		NB.encodeInt32(b, 0, h.a);
-		NB.encodeInt32(b, 4, h.b);
-		NB.encodeInt32(b, 8, h.c);
-		NB.encodeInt32(b, 12, h.d);
-		NB.encodeInt32(b, 16, h.e);
-		return b;
-	}
+	public abstract byte[] digest() throws Sha1CollisionException;
 
 	/**
 	 * Finish the digest and return the resulting hash.
@@ -505,10 +146,7 @@ public class SHA1 {
 	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
-	public ObjectId toObjectId() throws Sha1CollisionException {
-		finish();
-		return h.toObjectId();
-	}
+	public abstract ObjectId toObjectId() throws Sha1CollisionException;
 
 	/**
 	 * Finish the digest and return the resulting hash.
@@ -520,60 +158,42 @@ public class SHA1 {
 	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
 	 *             if a collision was detected and safeHash is false.
 	 */
-	public void digest(MutableObjectId id) throws Sha1CollisionException {
-		finish();
-		id.set(h.a, h.b, h.c, h.d, h.e);
-	}
+	public abstract void digest(MutableObjectId id)
+			throws Sha1CollisionException;
 
 	/**
-	 * Check if a collision was detected.
+	 * Reset this instance to compute another hash.
 	 *
+	 * @return {@code this}.
+	 */
+	public abstract SHA1 reset();
+
+	/**
+	 * Enable likely collision detection.
+	 * <p>
+	 * Default for implementations supporting collision detection is
+	 * {@code true}.
 	 * <p>
-	 * This method only returns an accurate result after the digest was obtained
-	 * through {@link #digest()}, {@link #digest(MutableObjectId)} or
-	 * {@link #toObjectId()}, as the hashing function must finish processing to
-	 * know the final state.
+	 * Implementations not supporting collision detection ignore calls to this
+	 * method.
 	 *
-	 * @return {@code true} if a likely collision was detected.
+	 * @param detect
+	 *            a boolean.
+	 * @return {@code this}
 	 */
-	public boolean hasCollision() {
-		return foundCollision;
-	}
+	public abstract SHA1 setDetectCollision(boolean detect);
 
 	/**
-	 * Reset this instance to compute another hash.
+	 * Check if a collision was detected. This method only returns an accurate
+	 * result after the digest was obtained through {@link #digest()},
+	 * {@link #digest(MutableObjectId)} or {@link #toObjectId()}, as the hashing
+	 * function must finish processing to know the final state.
+	 * <p>
+	 * Implementations not supporting collision detection always return
+	 * {@code false}.
+	 * <p>
 	 *
-	 * @return {@code this}.
+	 * @return {@code true} if a likely collision was detected.
 	 */
-	public SHA1 reset() {
-		h.init();
-		length = 0;
-		foundCollision = false;
-		return this;
-	}
-
-	private static final class State {
-		int a;
-		int b;
-		int c;
-		int d;
-		int e;
-
-		final void init() {
-			// Magic initialization constants defined by FIPS180.
-			save(0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0);
-		}
-
-		final void save(int a1, int b1, int c1, int d1, int e1) {
-			a = a1;
-			b = b1;
-			c = c1;
-			d = d1;
-			e = e1;
-		}
-
-		ObjectId toObjectId() {
-			return new ObjectId(a, b, c, d, e);
-		}
-	}
-}
+	public abstract boolean hasCollision();
+}
\ No newline at end of file
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Java.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Java.java
new file mode 100644
index 0000000000..213ee97531
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Java.java
@@ -0,0 +1,579 @@
+/*
+ * Copyright (C) 2017, Google Inc. and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.util.sha1;
+
+import static java.lang.Integer.lowestOneBit;
+import static java.lang.Integer.numberOfTrailingZeros;
+import static java.lang.Integer.rotateLeft;
+import static java.lang.Integer.rotateRight;
+
+import java.text.MessageFormat;
+import java.util.Arrays;
+
+import org.eclipse.jgit.internal.JGitText;
+import org.eclipse.jgit.lib.MutableObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.util.NB;
+import org.eclipse.jgit.util.SystemReader;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Pure Java implementation of SHA-1 from FIPS 180-1 / RFC 3174.
+ *
+ * <p>
+ * See <a href="https://tools.ietf.org/html/rfc3174">RFC 3174</a>.
+ * <p>
+ * Unlike MessageDigest, this implementation includes the algorithm used by
+ * {@code sha1dc} to detect cryptanalytic collision attacks against SHA-1, such
+ * as the one used by <a href="https://shattered.it/">SHAttered</a>. See
+ * <a href="https://github.com/cr-marcstevens/sha1collisiondetection">
+ * sha1collisiondetection</a> for more information.
+ * <p>
+ * When detectCollision is true (default), this implementation throws
+ * {@link org.eclipse.jgit.util.sha1.Sha1CollisionException} from any digest
+ * method if a potential collision was detected.
+ *
+ * @since 4.7
+ */
+class SHA1Java extends SHA1 {
+	private static final Logger LOG = LoggerFactory.getLogger(SHA1Java.class);
+	private static final boolean DETECT_COLLISIONS;
+
+	static {
+		SystemReader sr = SystemReader.getInstance();
+		String v = sr.getProperty("org.eclipse.jgit.util.sha1.detectCollision"); //$NON-NLS-1$
+		DETECT_COLLISIONS = v != null ? Boolean.parseBoolean(v) : true;
+	}
+
+	private final State h = new State();
+	private final int[] w = new int[80];
+
+	/** Buffer to accumulate partial blocks to 64 byte alignment. */
+	private final byte[] buffer = new byte[64];
+
+	/** Total number of bytes in the message. */
+	private long length;
+
+	private boolean detectCollision = DETECT_COLLISIONS;
+	private boolean foundCollision;
+
+	private final int[] w2 = new int[80];
+	private final State state58 = new State();
+	private final State state65 = new State();
+	private final State hIn = new State();
+	private final State hTmp = new State();
+
+	SHA1Java() {
+		h.init();
+	}
+
+	/**
+	 * Enable likely collision detection.
+	 * <p>
+	 * Default is {@code true}.
+	 * <p>
+	 * May also be set by system property:
+	 * {@code -Dorg.eclipse.jgit.util.sha1.detectCollision=true}.
+	 *
+	 * @param detect
+	 *            a boolean.
+	 * @return {@code this}
+	 */
+	@Override
+	public SHA1 setDetectCollision(boolean detect) {
+		detectCollision = detect;
+		return this;
+	}
+
+	/**
+	 * Update the digest computation by adding a byte.
+	 *
+	 * @param b a byte.
+	 */
+	@Override
+	public void update(byte b) {
+		int bufferLen = (int) (length & 63);
+		length++;
+		buffer[bufferLen] = b;
+		if (bufferLen == 63) {
+			compress(buffer, 0);
+		}
+	}
+
+	/**
+	 * Update the digest computation by adding bytes to the message.
+	 *
+	 * @param in
+	 *            input array of bytes.
+	 */
+	@Override
+	public void update(byte[] in) {
+		update(in, 0, in.length);
+	}
+
+	/**
+	 * Update the digest computation by adding bytes to the message.
+	 *
+	 * @param in
+	 *            input array of bytes.
+	 * @param p
+	 *            offset to start at from {@code in}.
+	 * @param len
+	 *            number of bytes to hash.
+	 */
+	@Override
+	public void update(byte[] in, int p, int len) {
+		// SHA-1 compress can only process whole 64 byte blocks.
+		// Hold partial updates in buffer, whose length is the low bits.
+		int bufferLen = (int) (length & 63);
+		length += len;
+
+		if (bufferLen > 0) {
+			int n = Math.min(64 - bufferLen, len);
+			System.arraycopy(in, p, buffer, bufferLen, n);
+			p += n;
+			len -= n;
+			if (bufferLen + n < 64) {
+				return;
+			}
+			compress(buffer, 0);
+		}
+		while (len >= 64) {
+			compress(in, p);
+			p += 64;
+			len -= 64;
+		}
+		if (len > 0) {
+			System.arraycopy(in, p, buffer, 0, len);
+		}
+	}
+
+	private void compress(byte[] block, int p) {
+		initBlock(block, p);
+		int ubcDvMask = detectCollision ? UbcCheck.check(w) : 0;
+		compress();
+
+		while (ubcDvMask != 0) {
+			int b = numberOfTrailingZeros(lowestOneBit(ubcDvMask));
+			UbcCheck.DvInfo dv = UbcCheck.DV[b];
+			for (int i = 0; i < 80; i++) {
+				w2[i] = w[i] ^ dv.dm[i];
+			}
+			recompress(dv.testt);
+			if (eq(hTmp, h)) {
+				foundCollision = true;
+				break;
+			}
+			ubcDvMask &= ~(1 << b);
+		}
+	}
+
+	private void initBlock(byte[] block, int p) {
+		for (int t = 0; t < 16; t++) {
+			w[t] = NB.decodeInt32(block, p + (t << 2));
+		}
+
+		// RFC 3174 6.1.b, extend state vector to 80 words.
+		for (int t = 16; t < 80; t++) {
+			int x = w[t - 3] ^ w[t - 8] ^ w[t - 14] ^ w[t - 16];
+			w[t] = rotateLeft(x, 1); // S^1(...)
+		}
+	}
+
+	private void compress() {
+		// Method 1 from RFC 3174 section 6.1.
+		// Method 2 (circular queue of 16 words) is slower.
+		int a = h.a, b = h.b, c = h.c, d = h.d, e = h.e;
+
+		// @formatter:off
+		 e += s1(a, b, c, d,w[ 0]);  b = rotateLeft( b, 30);
+		 d += s1(e, a, b, c,w[ 1]);  a = rotateLeft( a, 30);
+		 c += s1(d, e, a, b,w[ 2]);  e = rotateLeft( e, 30);
+		 b += s1(c, d, e, a,w[ 3]);  d = rotateLeft( d, 30);
+		 a += s1(b, c, d, e,w[ 4]);  c = rotateLeft( c, 30);
+		 e += s1(a, b, c, d,w[ 5]);  b = rotateLeft( b, 30);
+		 d += s1(e, a, b, c,w[ 6]);  a = rotateLeft( a, 30);
+		 c += s1(d, e, a, b,w[ 7]);  e = rotateLeft( e, 30);
+		 b += s1(c, d, e, a,w[ 8]);  d = rotateLeft( d, 30);
+		 a += s1(b, c, d, e,w[ 9]);  c = rotateLeft( c, 30);
+		 e += s1(a, b, c, d,w[ 10]);  b = rotateLeft( b, 30);
+		 d += s1(e, a, b, c,w[ 11]);  a = rotateLeft( a, 30);
+		 c += s1(d, e, a, b,w[ 12]);  e = rotateLeft( e, 30);
+		 b += s1(c, d, e, a,w[ 13]);  d = rotateLeft( d, 30);
+		 a += s1(b, c, d, e,w[ 14]);  c = rotateLeft( c, 30);
+		 e += s1(a, b, c, d,w[ 15]);  b = rotateLeft( b, 30);
+		 d += s1(e, a, b, c,w[ 16]);  a = rotateLeft( a, 30);
+		 c += s1(d, e, a, b,w[ 17]);  e = rotateLeft( e, 30);
+		 b += s1(c, d, e, a,w[ 18]);  d = rotateLeft( d, 30);
+		 a += s1(b, c, d, e,w[ 19]);  c = rotateLeft( c, 30);
+
+		 e += s2(a, b, c, d,w[ 20]);  b = rotateLeft( b, 30);
+		 d += s2(e, a, b, c,w[ 21]);  a = rotateLeft( a, 30);
+		 c += s2(d, e, a, b,w[ 22]);  e = rotateLeft( e, 30);
+		 b += s2(c, d, e, a,w[ 23]);  d = rotateLeft( d, 30);
+		 a += s2(b, c, d, e,w[ 24]);  c = rotateLeft( c, 30);
+		 e += s2(a, b, c, d,w[ 25]);  b = rotateLeft( b, 30);
+		 d += s2(e, a, b, c,w[ 26]);  a = rotateLeft( a, 30);
+		 c += s2(d, e, a, b,w[ 27]);  e = rotateLeft( e, 30);
+		 b += s2(c, d, e, a,w[ 28]);  d = rotateLeft( d, 30);
+		 a += s2(b, c, d, e,w[ 29]);  c = rotateLeft( c, 30);
+		 e += s2(a, b, c, d,w[ 30]);  b = rotateLeft( b, 30);
+		 d += s2(e, a, b, c,w[ 31]);  a = rotateLeft( a, 30);
+		 c += s2(d, e, a, b,w[ 32]);  e = rotateLeft( e, 30);
+		 b += s2(c, d, e, a,w[ 33]);  d = rotateLeft( d, 30);
+		 a += s2(b, c, d, e,w[ 34]);  c = rotateLeft( c, 30);
+		 e += s2(a, b, c, d,w[ 35]);  b = rotateLeft( b, 30);
+		 d += s2(e, a, b, c,w[ 36]);  a = rotateLeft( a, 30);
+		 c += s2(d, e, a, b,w[ 37]);  e = rotateLeft( e, 30);
+		 b += s2(c, d, e, a,w[ 38]);  d = rotateLeft( d, 30);
+		 a += s2(b, c, d, e,w[ 39]);  c = rotateLeft( c, 30);
+
+		 e += s3(a, b, c, d,w[ 40]);  b = rotateLeft( b, 30);
+		 d += s3(e, a, b, c,w[ 41]);  a = rotateLeft( a, 30);
+		 c += s3(d, e, a, b,w[ 42]);  e = rotateLeft( e, 30);
+		 b += s3(c, d, e, a,w[ 43]);  d = rotateLeft( d, 30);
+		 a += s3(b, c, d, e,w[ 44]);  c = rotateLeft( c, 30);
+		 e += s3(a, b, c, d,w[ 45]);  b = rotateLeft( b, 30);
+		 d += s3(e, a, b, c,w[ 46]);  a = rotateLeft( a, 30);
+		 c += s3(d, e, a, b,w[ 47]);  e = rotateLeft( e, 30);
+		 b += s3(c, d, e, a,w[ 48]);  d = rotateLeft( d, 30);
+		 a += s3(b, c, d, e,w[ 49]);  c = rotateLeft( c, 30);
+		 e += s3(a, b, c, d,w[ 50]);  b = rotateLeft( b, 30);
+		 d += s3(e, a, b, c,w[ 51]);  a = rotateLeft( a, 30);
+		 c += s3(d, e, a, b,w[ 52]);  e = rotateLeft( e, 30);
+		 b += s3(c, d, e, a,w[ 53]);  d = rotateLeft( d, 30);
+		 a += s3(b, c, d, e,w[ 54]);  c = rotateLeft( c, 30);
+		 e += s3(a, b, c, d,w[ 55]);  b = rotateLeft( b, 30);
+		 d += s3(e, a, b, c,w[ 56]);  a = rotateLeft( a, 30);
+		 c += s3(d, e, a, b,w[ 57]);  e = rotateLeft( e, 30);
+		state58.save(a, b, c, d, e);
+		 b += s3(c, d, e, a,w[ 58]);  d = rotateLeft( d, 30);
+		 a += s3(b, c, d, e,w[ 59]);  c = rotateLeft( c, 30);
+
+		 e += s4(a, b, c, d,w[ 60]);  b = rotateLeft( b, 30);
+		 d += s4(e, a, b, c,w[ 61]);  a = rotateLeft( a, 30);
+		 c += s4(d, e, a, b,w[ 62]);  e = rotateLeft( e, 30);
+		 b += s4(c, d, e, a,w[ 63]);  d = rotateLeft( d, 30);
+		 a += s4(b, c, d, e,w[ 64]);  c = rotateLeft( c, 30);
+		state65.save(a, b, c, d, e);
+		 e += s4(a, b, c, d,w[ 65]);  b = rotateLeft( b, 30);
+		 d += s4(e, a, b, c,w[ 66]);  a = rotateLeft( a, 30);
+		 c += s4(d, e, a, b,w[ 67]);  e = rotateLeft( e, 30);
+		 b += s4(c, d, e, a,w[ 68]);  d = rotateLeft( d, 30);
+		 a += s4(b, c, d, e,w[ 69]);  c = rotateLeft( c, 30);
+		 e += s4(a, b, c, d,w[ 70]);  b = rotateLeft( b, 30);
+		 d += s4(e, a, b, c,w[ 71]);  a = rotateLeft( a, 30);
+		 c += s4(d, e, a, b,w[ 72]);  e = rotateLeft( e, 30);
+		 b += s4(c, d, e, a,w[ 73]);  d = rotateLeft( d, 30);
+		 a += s4(b, c, d, e,w[ 74]);  c = rotateLeft( c, 30);
+		 e += s4(a, b, c, d,w[ 75]);  b = rotateLeft( b, 30);
+		 d += s4(e, a, b, c,w[ 76]);  a = rotateLeft( a, 30);
+		 c += s4(d, e, a, b,w[ 77]);  e = rotateLeft( e, 30);
+		 b += s4(c, d, e, a,w[ 78]);  d = rotateLeft( d, 30);
+		 a += s4(b, c, d, e,w[ 79]);  c = rotateLeft( c, 30);
+
+		// @formatter:on
+		h.save(h.a + a, h.b + b, h.c + c, h.d + d, h.e + e);
+	}
+
+	private void recompress(int t) {
+		State s;
+		switch (t) {
+		case 58:
+			s = state58;
+			break;
+		case 65:
+			s = state65;
+			break;
+		default:
+			throw new IllegalStateException();
+		}
+		int a = s.a, b = s.b, c = s.c, d = s.d, e = s.e;
+
+		// @formatter:off
+	  if (t == 65) {
+		{ c = rotateRight( c, 30);  a -= s4(b, c, d, e,w2[ 64]);}
+		{ d = rotateRight( d, 30);  b -= s4(c, d, e, a,w2[ 63]);}
+		{ e = rotateRight( e, 30);  c -= s4(d, e, a, b,w2[ 62]);}
+		{ a = rotateRight( a, 30);  d -= s4(e, a, b, c,w2[ 61]);}
+		{ b = rotateRight( b, 30);  e -= s4(a, b, c, d,w2[ 60]);}
+
+		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 59]);}
+		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 58]);}
+	  }
+		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 57]);}
+		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 56]);}
+		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 55]);}
+		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 54]);}
+		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 53]);}
+		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 52]);}
+		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 51]);}
+		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 50]);}
+		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 49]);}
+		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 48]);}
+		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 47]);}
+		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 46]);}
+		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 45]);}
+		{ c = rotateRight( c, 30);  a -= s3(b, c, d, e,w2[ 44]);}
+		{ d = rotateRight( d, 30);  b -= s3(c, d, e, a,w2[ 43]);}
+		{ e = rotateRight( e, 30);  c -= s3(d, e, a, b,w2[ 42]);}
+		{ a = rotateRight( a, 30);  d -= s3(e, a, b, c,w2[ 41]);}
+		{ b = rotateRight( b, 30);  e -= s3(a, b, c, d,w2[ 40]);}
+
+		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 39]);}
+		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 38]);}
+		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 37]);}
+		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 36]);}
+		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 35]);}
+		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 34]);}
+		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 33]);}
+		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 32]);}
+		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 31]);}
+		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 30]);}
+		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 29]);}
+		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 28]);}
+		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 27]);}
+		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 26]);}
+		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 25]);}
+		{ c = rotateRight( c, 30);  a -= s2(b, c, d, e,w2[ 24]);}
+		{ d = rotateRight( d, 30);  b -= s2(c, d, e, a,w2[ 23]);}
+		{ e = rotateRight( e, 30);  c -= s2(d, e, a, b,w2[ 22]);}
+		{ a = rotateRight( a, 30);  d -= s2(e, a, b, c,w2[ 21]);}
+		{ b = rotateRight( b, 30);  e -= s2(a, b, c, d,w2[ 20]);}
+
+		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 19]);}
+		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 18]);}
+		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 17]);}
+		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 16]);}
+		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 15]);}
+		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 14]);}
+		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 13]);}
+		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 12]);}
+		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 11]);}
+		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 10]);}
+		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 9]);}
+		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 8]);}
+		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 7]);}
+		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 6]);}
+		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 5]);}
+		{ c = rotateRight( c, 30);  a -= s1(b, c, d, e,w2[ 4]);}
+		{ d = rotateRight( d, 30);  b -= s1(c, d, e, a,w2[ 3]);}
+		{ e = rotateRight( e, 30);  c -= s1(d, e, a, b,w2[ 2]);}
+		{ a = rotateRight( a, 30);  d -= s1(e, a, b, c,w2[ 1]);}
+		{ b = rotateRight( b, 30);  e -= s1(a, b, c, d,w2[ 0]);}
+
+		hIn.save(a, b, c, d, e);
+		a = s.a; b = s.b; c = s.c; d = s.d; e = s.e;
+
+	  if (t == 58) {
+		{ b += s3(c, d, e, a,w2[ 58]);  d = rotateLeft( d, 30);}
+		{ a += s3(b, c, d, e,w2[ 59]);  c = rotateLeft( c, 30);}
+
+		{ e += s4(a, b, c, d,w2[ 60]);  b = rotateLeft( b, 30);}
+		{ d += s4(e, a, b, c,w2[ 61]);  a = rotateLeft( a, 30);}
+		{ c += s4(d, e, a, b,w2[ 62]);  e = rotateLeft( e, 30);}
+		{ b += s4(c, d, e, a,w2[ 63]);  d = rotateLeft( d, 30);}
+		{ a += s4(b, c, d, e,w2[ 64]);  c = rotateLeft( c, 30);}
+	  }
+		{ e += s4(a, b, c, d,w2[ 65]);  b = rotateLeft( b, 30);}
+		{ d += s4(e, a, b, c,w2[ 66]);  a = rotateLeft( a, 30);}
+		{ c += s4(d, e, a, b,w2[ 67]);  e = rotateLeft( e, 30);}
+		{ b += s4(c, d, e, a,w2[ 68]);  d = rotateLeft( d, 30);}
+		{ a += s4(b, c, d, e,w2[ 69]);  c = rotateLeft( c, 30);}
+		{ e += s4(a, b, c, d,w2[ 70]);  b = rotateLeft( b, 30);}
+		{ d += s4(e, a, b, c,w2[ 71]);  a = rotateLeft( a, 30);}
+		{ c += s4(d, e, a, b,w2[ 72]);  e = rotateLeft( e, 30);}
+		{ b += s4(c, d, e, a,w2[ 73]);  d = rotateLeft( d, 30);}
+		{ a += s4(b, c, d, e,w2[ 74]);  c = rotateLeft( c, 30);}
+		{ e += s4(a, b, c, d,w2[ 75]);  b = rotateLeft( b, 30);}
+		{ d += s4(e, a, b, c,w2[ 76]);  a = rotateLeft( a, 30);}
+		{ c += s4(d, e, a, b,w2[ 77]);  e = rotateLeft( e, 30);}
+		{ b += s4(c, d, e, a,w2[ 78]);  d = rotateLeft( d, 30);}
+		{ a += s4(b, c, d, e,w2[ 79]);  c = rotateLeft( c, 30);}
+
+		// @formatter:on
+		hTmp.save(hIn.a + a, hIn.b + b, hIn.c + c, hIn.d + d, hIn.e + e);
+	}
+
+	private static int s1(int a, int b, int c, int d, int w_t) {
+		return rotateLeft(a, 5)
+				// f: 0 <= t <= 19
+				+ ((b & c) | ((~b) & d))
+				+ 0x5A827999 + w_t;
+	}
+
+	private static int s2(int a, int b, int c, int d, int w_t) {
+		return rotateLeft(a, 5)
+				// f: 20 <= t <= 39
+				+ (b ^ c ^ d)
+				+ 0x6ED9EBA1 + w_t;
+	}
+
+	private static int s3(int a, int b, int c, int d, int w_t) {
+		return rotateLeft(a, 5)
+				// f: 40 <= t <= 59
+				+ ((b & c) | (b & d) | (c & d))
+				+ 0x8F1BBCDC + w_t;
+	}
+
+	private static int s4(int a, int b, int c, int d, int w_t) {
+		return rotateLeft(a, 5)
+				// f: 60 <= t <= 79
+				+ (b ^ c ^ d)
+				+ 0xCA62C1D6 + w_t;
+	}
+
+	private static boolean eq(State q, State r) {
+		return q.a == r.a
+				&& q.b == r.b
+				&& q.c == r.c
+				&& q.d == r.d
+				&& q.e == r.e;
+	}
+
+	private void finish() {
+		int bufferLen = (int) (length & 63);
+		if (bufferLen > 55) {
+			// Last block is too small; pad, compress, pad another block.
+			buffer[bufferLen++] = (byte) 0x80;
+			Arrays.fill(buffer, bufferLen, 64, (byte) 0);
+			compress(buffer, 0);
+			Arrays.fill(buffer, 0, 56, (byte) 0);
+		} else {
+			// Last block can hold padding and length.
+			buffer[bufferLen++] = (byte) 0x80;
+			Arrays.fill(buffer, bufferLen, 56, (byte) 0);
+		}
+
+		// SHA-1 appends the length of the message in bits after the
+		// padding block (above). Here length is in bytes. Multiply by
+		// 8 by shifting by 3 as part of storing the 64 bit byte length
+		// into the two words expected in the trailer.
+		NB.encodeInt32(buffer, 56, (int) (length >>> (32 - 3)));
+		NB.encodeInt32(buffer, 60, (int) (length << 3));
+		compress(buffer, 0);
+
+		if (foundCollision) {
+			ObjectId id = h.toObjectId();
+			LOG.warn(MessageFormat.format(JGitText.get().sha1CollisionDetected,
+					id.name()));
+			throw new Sha1CollisionException(id);
+		}
+	}
+
+	/**
+	 * Finish the digest and return the resulting hash.
+	 * <p>
+	 * Once {@code digest()} is called, this instance should be discarded.
+	 *
+	 * @return the bytes for the resulting hash.
+	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
+	 *             if a collision was detected and safeHash is false.
+	 */
+	@Override
+	public byte[] digest() throws Sha1CollisionException {
+		finish();
+
+		byte[] b = new byte[20];
+		NB.encodeInt32(b, 0, h.a);
+		NB.encodeInt32(b, 4, h.b);
+		NB.encodeInt32(b, 8, h.c);
+		NB.encodeInt32(b, 12, h.d);
+		NB.encodeInt32(b, 16, h.e);
+		return b;
+	}
+
+	/**
+	 * Finish the digest and return the resulting hash.
+	 * <p>
+	 * Once {@code digest()} is called, this instance should be discarded.
+	 *
+	 * @return the ObjectId for the resulting hash.
+	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
+	 *             if a collision was detected and safeHash is false.
+	 */
+	@Override
+	public ObjectId toObjectId() throws Sha1CollisionException {
+		finish();
+		return h.toObjectId();
+	}
+
+	/**
+	 * Finish the digest and return the resulting hash.
+	 * <p>
+	 * Once {@code digest()} is called, this instance should be discarded.
+	 *
+	 * @param id
+	 *            destination to copy the digest to.
+	 * @throws org.eclipse.jgit.util.sha1.Sha1CollisionException
+	 *             if a collision was detected and safeHash is false.
+	 */
+	@Override
+	public void digest(MutableObjectId id) throws Sha1CollisionException {
+		finish();
+		id.set(h.a, h.b, h.c, h.d, h.e);
+	}
+
+	/**
+	 * Check if a collision was detected.
+	 *
+	 * <p>
+	 * This method only returns an accurate result after the digest was obtained
+	 * through {@link #digest()}, {@link #digest(MutableObjectId)} or
+	 * {@link #toObjectId()}, as the hashing function must finish processing to
+	 * know the final state.
+	 *
+	 * @return {@code true} if a likely collision was detected.
+	 */
+	@Override
+	public boolean hasCollision() {
+		return foundCollision;
+	}
+
+	/**
+	 * Reset this instance to compute another hash.
+	 *
+	 * @return {@code this}.
+	 */
+	@Override
+	public SHA1 reset() {
+		h.init();
+		length = 0;
+		foundCollision = false;
+		return this;
+	}
+
+	private static final class State {
+		int a;
+		int b;
+		int c;
+		int d;
+		int e;
+
+		final void init() {
+			// Magic initialization constants defined by FIPS180.
+			save(0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476, 0xC3D2E1F0);
+		}
+
+		final void save(int a1, int b1, int c1, int d1, int e1) {
+			a = a1;
+			b = b1;
+			c = c1;
+			d = d1;
+			e = e1;
+		}
+
+		ObjectId toObjectId() {
+			return new ObjectId(a, b, c, d, e);
+		}
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Native.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Native.java
new file mode 100644
index 0000000000..4599ac0cba
--- /dev/null
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/SHA1Native.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2022, Matthias Sohn <matthias.sohn@sap.com> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.util.sha1;
+
+import java.security.MessageDigest;
+
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.MutableObjectId;
+import org.eclipse.jgit.lib.ObjectId;
+
+/**
+ * SHA1 implementation using native implementation from JDK. It doesn't support
+ * collision detection but is faster than the pure Java implementation.
+ */
+class SHA1Native extends SHA1 {
+
+	private final MessageDigest md;
+
+	SHA1Native() {
+		md = Constants.newMessageDigest();
+	}
+
+	@Override
+	public void update(byte b) {
+		md.update(b);
+	}
+
+	@Override
+	public void update(byte[] in) {
+		md.update(in);
+	}
+
+	@Override
+	public void update(byte[] in, int p, int len) {
+		md.update(in, p, len);
+	}
+
+	@Override
+	public byte[] digest() throws Sha1CollisionException {
+		return md.digest();
+	}
+
+	@Override
+	public ObjectId toObjectId() throws Sha1CollisionException {
+		return ObjectId.fromRaw(md.digest());
+	}
+
+	@Override
+	public void digest(MutableObjectId id) throws Sha1CollisionException {
+		id.fromRaw(md.digest());
+	}
+
+	@Override
+	public SHA1 reset() {
+		md.reset();
+		return this;
+	}
+
+	@Override
+	public SHA1 setDetectCollision(boolean detect) {
+		return this;
+	}
+
+	@Override
+	public boolean hasCollision() {
+		return false;
+	}
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/Sha1CollisionException.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/Sha1CollisionException.java
index ce95ba5e85..fc8d7ab9f9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/Sha1CollisionException.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/sha1/Sha1CollisionException.java
@@ -16,7 +16,7 @@ import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.lib.ObjectId;
 
 /**
- * Thrown by {@link org.eclipse.jgit.util.sha1.SHA1} if it detects a likely hash
+ * Thrown by {@link org.eclipse.jgit.util.sha1.SHA1Java} if it detects a likely hash
  * collision.
  *
  * @since 4.7
-- 
2.39.5