From 3fc31cc8724885d8d0f2d7ff8028f3b4f6b49c8e Mon Sep 17 00:00:00 2001
From: Vsevolod Stakhov <vsevolod@highsecure.ru>
Date: Sat, 19 May 2018 14:50:43 +0100
Subject: [PATCH] [Minor] Add method to decrypt data using keypair

---
 src/libcryptobox/keypair.c | 69 ++++++++++++++++++++++++++++++++++++++
 src/libcryptobox/keypair.h | 17 ++++++++++
 2 files changed, 86 insertions(+)

diff --git a/src/libcryptobox/keypair.c b/src/libcryptobox/keypair.c
index 98401e10f..1f8acc6d1 100644
--- a/src/libcryptobox/keypair.c
+++ b/src/libcryptobox/keypair.c
@@ -20,6 +20,8 @@
 #include "libutil/str_util.h"
 #include "libutil/printf.h"
 
+const guchar encrypted_magic[7] = {'r', 'u', 'c', 'l', 'e', 'v', '1'};
+
 static GQuark
 rspamd_keypair_quark (void)
 {
@@ -908,3 +910,70 @@ rspamd_pubkey_equal (const struct rspamd_cryptobox_pubkey *k1,
 
 	return FALSE;
 }
+
+gboolean
+rspamd_keypair_decrypt (struct rspamd_cryptobox_keypair *kp,
+						const guchar *in, gsize inlen,
+						guchar **out, gsize *outlen,
+						GError **err)
+{
+	const guchar *nonce, *mac, *data, *pubkey;
+
+	g_assert (kp != NULL);
+	g_assert (in != NULL);
+
+	if (kp->type != RSPAMD_KEYPAIR_KEX) {
+		g_set_error (err, rspamd_keypair_quark (), EINVAL,
+				"invalid keypair type");
+
+		return FALSE;
+	}
+
+	if (inlen < sizeof (encrypted_magic) + rspamd_cryptobox_pk_bytes (kp->alg) +
+				rspamd_cryptobox_mac_bytes (kp->alg) +
+				rspamd_cryptobox_nonce_bytes (kp->alg)) {
+		g_set_error (err, rspamd_keypair_quark (), E2BIG, "invalid size: too small");
+
+		return FALSE;
+	}
+
+	if (memcmp (in, encrypted_magic, sizeof (encrypted_magic)) != 0) {
+		g_set_error (err, rspamd_keypair_quark (), EINVAL,
+				"invalid magic");
+
+		return FALSE;
+	}
+
+	/* Set pointers */
+	pubkey = in + sizeof (encrypted_magic);
+	mac = pubkey + rspamd_cryptobox_pk_bytes (kp->alg);
+	nonce = mac + rspamd_cryptobox_mac_bytes (kp->alg);
+	data = nonce + rspamd_cryptobox_nonce_bytes (kp->alg);
+
+	if (data - in >= inlen) {
+		g_set_error (err, rspamd_keypair_quark (), E2BIG, "invalid size: too small");
+
+		return FALSE;
+	}
+
+	inlen -= data - in;
+
+	/* Allocate memory for output */
+	*out = g_malloc (inlen);
+	memcpy (*out, data, inlen);
+
+	if (!rspamd_cryptobox_decrypt_inplace (*out, inlen, nonce, pubkey,
+			rspamd_keypair_component (kp, RSPAMD_KEYPAIR_COMPONENT_SK, NULL),
+			mac, kp->alg)) {
+		g_set_error (err, rspamd_keypair_quark (), EPERM, "verification failed");
+		g_free (*out);
+
+		return FALSE;
+	}
+
+	if (outlen) {
+		*outlen = inlen;
+	}
+
+	return TRUE;
+}
diff --git a/src/libcryptobox/keypair.h b/src/libcryptobox/keypair.h
index b24ecc9aa..fc17412e2 100644
--- a/src/libcryptobox/keypair.h
+++ b/src/libcryptobox/keypair.h
@@ -28,6 +28,8 @@ enum rspamd_cryptobox_keypair_type {
 	RSPAMD_KEYPAIR_SIGN
 };
 
+extern const guchar encrypted_magic[7];
+
 /**
  * Opaque structure for the full (public + private) keypair
  */
@@ -270,5 +272,20 @@ gboolean rspamd_keypair_verify (struct rspamd_cryptobox_pubkey *pk,
 gboolean rspamd_pubkey_equal (const struct rspamd_cryptobox_pubkey *k1,
 		const struct rspamd_cryptobox_pubkey *k2);
 
+/**
+ * Decrypts data using keypair and a pubkey stored in in, in must start from
+ * `encrypted_magic` constant
+ * @param kp keypair
+ * @param in raw input
+ * @param inlen input length
+ * @param out output (allocated internally using g_malloc)
+ * @param outlen output size
+ * @return TRUE if decryption is completed, out must be freed in this case
+ */
+gboolean rspamd_keypair_decrypt (struct rspamd_cryptobox_keypair *kp,
+								 const guchar *in, gsize inlen,
+								 guchar **out, gsize *outlen,
+								 GError **err);
+
 
 #endif /* SRC_LIBCRYPTOBOX_KEYPAIR_H_ */
-- 
2.39.5