15 files changed, 775 insertions, 6 deletions
diff --git a/modules/auth/password/hash/argon2.go b/modules/auth/password/hash/argon2.go
new file mode 100644
index 0000000000..14c16b53c4
--- /dev/null
+++ b/modules/auth/password/hash/argon2.go
@@ -0,0 +1,80 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"encoding/hex"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"golang.org/x/crypto/argon2"
+)
+
+func init() {
+	Register("argon2", NewArgon2Hasher)
+}
+
+// Argon2Hasher implements PasswordHasher
+// and uses the Argon2 key derivation function, hybrant variant
+type Argon2Hasher struct {
+	time    uint32
+	memory  uint32
+	threads uint8
+	keyLen  uint32
+}
+
+// HashWithSaltBytes a provided password and salt
+func (hasher *Argon2Hasher) HashWithSaltBytes(password string, salt []byte) string {
+	if hasher == nil {
+		return ""
+	}
+	return hex.EncodeToString(argon2.IDKey([]byte(password), salt, hasher.time, hasher.memory, hasher.threads, hasher.keyLen))
+}
+
+// NewArgon2Hasher is a factory method to create an Argon2Hasher
+// The provided config should be either empty or of the form:
+// "<time>$<memory>$<threads>$<keyLen>", where <x> is the string representation
+// of an integer
+func NewArgon2Hasher(config string) *Argon2Hasher {
+	// This default configuration uses the following parameters:
+	// time=2, memory=64*1024, threads=8, keyLen=50.
+	// It will make two passes through the memory, using 64MiB in total.
+	// This matches the original configuration for `argon2` prior to storing hash parameters
+	// in the database.
+	// THESE VALUES MUST NOT BE CHANGED OR BACKWARDS COMPATIBILITY WILL BREAK
+	hasher := &Argon2Hasher{
+		time:    2,
+		memory:  1 << 16,
+		threads: 8,
+		keyLen:  50,
+	}
+
+	if config == "" {
+		return hasher
+	}
+
+	vals := strings.SplitN(config, "$", 4)
+	if len(vals) != 4 {
+		log.Error("invalid argon2 hash spec %s", config)
+		return nil
+	}
+
+	parsed, err := parseUIntParam(vals[0], "time", "argon2", config, nil)
+	hasher.time = uint32(parsed)
+
+	parsed, err = parseUIntParam(vals[1], "memory", "argon2", config, err)
+	hasher.memory = uint32(parsed)
+
+	parsed, err = parseUIntParam(vals[2], "threads", "argon2", config, err)
+	hasher.threads = uint8(parsed)
+
+	parsed, err = parseUIntParam(vals[3], "keyLen", "argon2", config, err)
+	hasher.keyLen = uint32(parsed)
+	if err != nil {
+		return nil
+	}
+
+	return hasher
+}
diff --git a/modules/auth/password/hash/bcrypt.go b/modules/auth/password/hash/bcrypt.go
new file mode 100644
index 0000000000..ddf5420408
--- /dev/null
+++ b/modules/auth/password/hash/bcrypt.go
@@ -0,0 +1,54 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"golang.org/x/crypto/bcrypt"
+)
+
+func init() {
+	Register("bcrypt", NewBcryptHasher)
+}
+
+// BcryptHasher implements PasswordHasher
+// and uses the bcrypt password hash function.
+type BcryptHasher struct {
+	cost int
+}
+
+// HashWithSaltBytes a provided password and salt
+func (hasher *BcryptHasher) HashWithSaltBytes(password string, salt []byte) string {
+	if hasher == nil {
+		return ""
+	}
+	hashedPassword, _ := bcrypt.GenerateFromPassword([]byte(password), hasher.cost)
+	return string(hashedPassword)
+}
+
+func (hasher *BcryptHasher) VerifyPassword(password, hashedPassword, salt string) bool {
+	return bcrypt.CompareHashAndPassword([]byte(hashedPassword), []byte(password)) == nil
+}
+
+// NewBcryptHasher is a factory method to create an BcryptHasher
+// The provided config should be either empty or the string representation of the "<cost>"
+// as an integer
+func NewBcryptHasher(config string) *BcryptHasher {
+	// This matches the original configuration for `bcrypt` prior to storing hash parameters
+	// in the database.
+	// THESE VALUES MUST NOT BE CHANGED OR BACKWARDS COMPATIBILITY WILL BREAK
+	hasher := &BcryptHasher{
+		cost: 10, // cost=10. i.e. 2^10 rounds of key expansion.
+	}
+
+	if config == "" {
+		return hasher
+	}
+	var err error
+	hasher.cost, err = parseIntParam(config, "cost", "bcrypt", config, nil)
+	if err != nil {
+		return nil
+	}
+
+	return hasher
+}
diff --git a/modules/auth/password/hash/common.go b/modules/auth/password/hash/common.go
new file mode 100644
index 0000000000..ac6faf35cf
--- /dev/null
+++ b/modules/auth/password/hash/common.go
@@ -0,0 +1,28 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"strconv"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+func parseIntParam(value, param, algorithmName, config string, previousErr error) (int, error) {
+	parsed, err := strconv.Atoi(value)
+	if err != nil {
+		log.Error("invalid integer for %s representation in %s hash spec %s", param, algorithmName, config)
+		return 0, err
+	}
+	return parsed, previousErr // <- Keep the previous error as this function should still return an error once everything has been checked if any call failed
+}
+
+func parseUIntParam(value, param, algorithmName, config string, previousErr error) (uint64, error) {
+	parsed, err := strconv.ParseUint(value, 10, 64)
+	if err != nil {
+		log.Error("invalid integer for %s representation in %s hash spec %s", param, algorithmName, config)
+		return 0, err
+	}
+	return parsed, previousErr // <- Keep the previous error as this function should still return an error once everything has been checked if any call failed
+}
diff --git a/modules/auth/password/hash/hash.go b/modules/auth/password/hash/hash.go
new file mode 100644
index 0000000000..3572dd46d4
--- /dev/null
+++ b/modules/auth/password/hash/hash.go
@@ -0,0 +1,180 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"crypto/subtle"
+	"encoding/hex"
+	"fmt"
+	"strings"
+	"sync/atomic"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+// This package takes care of hashing passwords, verifying passwords, defining
+// available password algorithms, defining recommended password algorithms and
+// choosing the default password algorithm.
+
+// PasswordSaltHasher will hash a provided password with the provided saltBytes
+type PasswordSaltHasher interface {
+	HashWithSaltBytes(password string, saltBytes []byte) string
+}
+
+// PasswordHasher will hash a provided password with the salt
+type PasswordHasher interface {
+	Hash(password, salt string) (string, error)
+}
+
+// PasswordVerifier will ensure that a providedPassword matches the hashPassword when hashed with the salt
+type PasswordVerifier interface {
+	VerifyPassword(providedPassword, hashedPassword, salt string) bool
+}
+
+// PasswordHashAlgorithms are named PasswordSaltHashers with a default verifier and hash function
+type PasswordHashAlgorithm struct {
+	PasswordSaltHasher
+	Specification string // The specification that is used to create the internal PasswordSaltHasher
+}
+
+// Hash the provided password with the salt and return the hash
+func (algorithm *PasswordHashAlgorithm) Hash(password, salt string) (string, error) {
+	var saltBytes []byte
+
+	// There are two formats for the salt value:
+	// * The new format is a (32+)-byte hex-encoded string
+	// * The old format was a 10-byte binary format
+	// We have to tolerate both here.
+	if len(salt) == 10 {
+		saltBytes = []byte(salt)
+	} else {
+		var err error
+		saltBytes, err = hex.DecodeString(salt)
+		if err != nil {
+			return "", err
+		}
+	}
+
+	return algorithm.HashWithSaltBytes(password, saltBytes), nil
+}
+
+// Verify the provided password matches the hashPassword when hashed with the salt
+func (algorithm *PasswordHashAlgorithm) VerifyPassword(providedPassword, hashedPassword, salt string) bool {
+	// Some PasswordSaltHashers have their own specialised compare function that takes into
+	// account the stored parameters within the hash. e.g. bcrypt
+	if verifier, ok := algorithm.PasswordSaltHasher.(PasswordVerifier); ok {
+		return verifier.VerifyPassword(providedPassword, hashedPassword, salt)
+	}
+
+	// Compute the hash of the password.
+	providedPasswordHash, err := algorithm.Hash(providedPassword, salt)
+	if err != nil {
+		log.Error("passwordhash: %v.Hash(): %v", algorithm.Specification, err)
+		return false
+	}
+
+	// Compare it against the hashed password in constant-time.
+	return subtle.ConstantTimeCompare([]byte(hashedPassword), []byte(providedPasswordHash)) == 1
+}
+
+var (
+	lastNonDefaultAlgorithm  atomic.Value
+	availableHasherFactories = map[string]func(string) PasswordSaltHasher{}
+)
+
+// Register registers a PasswordSaltHasher with the availableHasherFactories
+// Caution: This is not thread safe.
+func Register[T PasswordSaltHasher](name string, newFn func(config string) T) {
+	if _, has := availableHasherFactories[name]; has {
+		panic(fmt.Errorf("duplicate registration of password salt hasher: %s", name))
+	}
+
+	availableHasherFactories[name] = func(config string) PasswordSaltHasher {
+		n := newFn(config)
+		return n
+	}
+}
+
+// In early versions of gitea the password hash algorithm field of a user could be
+// empty. At that point the default was `pbkdf2` without configuration values
+//
+// Please note this is not the same as the DefaultAlgorithm which is used
+// to determine what an empty PASSWORD_HASH_ALGO setting in the app.ini means.
+// These are not the same even if they have the same apparent value and they mean different things.
+//
+// DO NOT COALESCE THESE VALUES
+const defaultEmptyHashAlgorithmSpecification = "pbkdf2"
+
+// Parse will convert the provided algorithm specification in to a PasswordHashAlgorithm
+// If the provided specification matches the DefaultHashAlgorithm Specification it will be
+// used.
+// In addition the last non-default hasher will be cached to help reduce the load from
+// parsing specifications.
+//
+// NOTE: No de-aliasing is done in this function, thus any specification which does not
+// contain a configuration will use the default values for that hasher. These are not
+// necessarily the same values as those obtained by dealiasing. This allows for
+// seamless backwards compatibility with the original configuration.
+//
+// To further labour this point, running `Parse("pbkdf2")` does not obtain the
+// same algorithm as setting `PASSWORD_HASH_ALGO=pbkdf2` in app.ini, nor is it intended to.
+// A user that has `password_hash_algo='pbkdf2'` in the db means get the original, unconfigured algorithm
+// Users will be migrated automatically as they log-in to have the complete specification stored
+// in their `password_hash_algo` fields by other code.
+func Parse(algorithmSpec string) *PasswordHashAlgorithm {
+	if algorithmSpec == "" {
+		algorithmSpec = defaultEmptyHashAlgorithmSpecification
+	}
+
+	if DefaultHashAlgorithm != nil && algorithmSpec == DefaultHashAlgorithm.Specification {
+		return DefaultHashAlgorithm
+	}
+
+	ptr := lastNonDefaultAlgorithm.Load()
+	if ptr != nil {
+		hashAlgorithm, ok := ptr.(*PasswordHashAlgorithm)
+		if ok && hashAlgorithm.Specification == algorithmSpec {
+			return hashAlgorithm
+		}
+	}
+
+	// Now convert the provided specification in to a hasherType +/- some configuration parameters
+	vals := strings.SplitN(algorithmSpec, "$", 2)
+	var hasherType string
+	var config string
+
+	if len(vals) == 0 {
+		// This should not happen as algorithmSpec should not be empty
+		// due to it being assigned to defaultEmptyHashAlgorithmSpecification above
+		// but we should be absolutely cautious here
+		return nil
+	}
+
+	hasherType = vals[0]
+	if len(vals) > 1 {
+		config = vals[1]
+	}
+
+	newFn, has := availableHasherFactories[hasherType]
+	if !has {
+		// unknown hasher type
+		return nil
+	}
+
+	ph := newFn(config)
+	if ph == nil {
+		// The provided configuration is likely invalid - it will have been logged already
+		// but we cannot hash safely
+		return nil
+	}
+
+	hashAlgorithm := &PasswordHashAlgorithm{
+		PasswordSaltHasher: ph,
+		Specification:      algorithmSpec,
+	}
+
+	lastNonDefaultAlgorithm.Store(hashAlgorithm)
+
+	return hashAlgorithm
+}
diff --git a/modules/auth/password/hash/hash_test.go b/modules/auth/password/hash/hash_test.go
new file mode 100644
index 0000000000..593c8386a3
--- /dev/null
+++ b/modules/auth/password/hash/hash_test.go
@@ -0,0 +1,186 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"encoding/hex"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type testSaltHasher string
+
+func (t testSaltHasher) HashWithSaltBytes(password string, salt []byte) string {
+	return password + "$" + string(salt) + "$" + string(t)
+}
+
+func Test_registerHasher(t *testing.T) {
+	Register("Test_registerHasher", func(config string) testSaltHasher {
+		return testSaltHasher(config)
+	})
+
+	assert.Panics(t, func() {
+		Register("Test_registerHasher", func(config string) testSaltHasher {
+			return testSaltHasher(config)
+		})
+	})
+
+	assert.Equal(t, "password$salt$",
+		Parse("Test_registerHasher").PasswordSaltHasher.HashWithSaltBytes("password", []byte("salt")))
+
+	assert.Equal(t, "password$salt$config",
+		Parse("Test_registerHasher$config").PasswordSaltHasher.HashWithSaltBytes("password", []byte("salt")))
+
+	delete(availableHasherFactories, "Test_registerHasher")
+}
+
+func TestParse(t *testing.T) {
+	hashAlgorithmsToTest := []string{}
+	for plainHashAlgorithmNames := range availableHasherFactories {
+		hashAlgorithmsToTest = append(hashAlgorithmsToTest, plainHashAlgorithmNames)
+	}
+	for _, aliased := range aliasAlgorithmNames {
+		if strings.Contains(aliased, "$") {
+			hashAlgorithmsToTest = append(hashAlgorithmsToTest, aliased)
+		}
+	}
+	for _, algorithmName := range hashAlgorithmsToTest {
+		t.Run(algorithmName, func(t *testing.T) {
+			algo := Parse(algorithmName)
+			assert.NotNil(t, algo, "Algorithm %s resulted in an empty algorithm", algorithmName)
+		})
+	}
+}
+
+func TestHashing(t *testing.T) {
+	hashAlgorithmsToTest := []string{}
+	for plainHashAlgorithmNames := range availableHasherFactories {
+		hashAlgorithmsToTest = append(hashAlgorithmsToTest, plainHashAlgorithmNames)
+	}
+	for _, aliased := range aliasAlgorithmNames {
+		if strings.Contains(aliased, "$") {
+			hashAlgorithmsToTest = append(hashAlgorithmsToTest, aliased)
+		}
+	}
+
+	runTests := func(password, salt string, shouldPass bool) {
+		for _, algorithmName := range hashAlgorithmsToTest {
+			t.Run(algorithmName, func(t *testing.T) {
+				output, err := Parse(algorithmName).Hash(password, salt)
+				if shouldPass {
+					assert.NoError(t, err)
+					assert.NotEmpty(t, output, "output for %s was empty", algorithmName)
+				} else {
+					assert.Error(t, err)
+				}
+
+				assert.Equal(t, Parse(algorithmName).VerifyPassword(password, output, salt), shouldPass)
+			})
+		}
+	}
+
+	// Test with new salt format.
+	runTests(strings.Repeat("a", 16), hex.EncodeToString([]byte{0x01, 0x02, 0x03}), true)
+
+	// Test with legacy salt format.
+	runTests(strings.Repeat("a", 16), strings.Repeat("b", 10), true)
+
+	// Test with invalid salt.
+	runTests(strings.Repeat("a", 16), "a", false)
+}
+
+// vectors were generated using the current codebase.
+var vectors = []struct {
+	algorithms []string
+	password   string
+	salt       string
+	output     string
+	shouldfail bool
+}{
+	{
+		algorithms: []string{"bcrypt", "bcrypt$10"},
+		password:   "abcdef",
+		salt:       strings.Repeat("a", 10),
+		output:     "$2a$10$fjtm8BsQ2crym01/piJroenO3oSVUBhSLKaGdTYJ4tG0ePVCrU0G2",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"scrypt", "scrypt$65536$16$2$50"},
+		password:   "abcdef",
+		salt:       strings.Repeat("a", 10),
+		output:     "3b571d0c07c62d42b7bad3dbf18fb0cd67d4d8cd4ad4c6928e1090e5b2a4a84437c6fd2627d897c0e7e65025ca62b67a0002",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"argon2", "argon2$2$65536$8$50"},
+		password:   "abcdef",
+		salt:       strings.Repeat("a", 10),
+		output:     "551f089f570f989975b6f7c6a8ff3cf89bc486dd7bbe87ed4d80ad4362f8ee599ec8dda78dac196301b98456402bcda775dc",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"pbkdf2", "pbkdf2$10000$50"},
+		password:   "abcdef",
+		salt:       strings.Repeat("a", 10),
+		output:     "ab48d5471b7e6ed42d10001db88c852ff7303c788e49da5c3c7b63d5adf96360303724b74b679223a3dea8a242d10abb1913",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"bcrypt", "bcrypt$10"},
+		password:   "abcdef",
+		salt:       hex.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04}),
+		output:     "$2a$10$qhgm32w9ZpqLygugWJsLjey8xRGcaq9iXAfmCeNBXxddgyoaOC3Gq",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"scrypt", "scrypt$65536$16$2$50"},
+		password:   "abcdef",
+		salt:       hex.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04}),
+		output:     "25fe5f66b43fa4eb7b6717905317cd2223cf841092dc8e0a1e8c75720ad4846cb5d9387303e14bc3c69faa3b1c51ef4b7de1",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"argon2", "argon2$2$65536$8$50"},
+		password:   "abcdef",
+		salt:       hex.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04}),
+		output:     "9c287db63a91d18bb1414b703216da4fc431387c1ae7c8acdb280222f11f0929831055dbfd5126a3b48566692e83ec750d2a",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"pbkdf2", "pbkdf2$10000$50"},
+		password:   "abcdef",
+		salt:       hex.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04}),
+		output:     "45d6cdc843d65cf0eda7b90ab41435762a282f7df013477a1c5b212ba81dbdca2edf1ecc4b5cb05956bb9e0c37ab29315d78",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"pbkdf2$320000$50"},
+		password:   "abcdef",
+		salt:       hex.EncodeToString([]byte{0x01, 0x02, 0x03, 0x04}),
+		output:     "84e233114499e8721da80e85568e5b7b5900b3e49a30845fcda9d1e1756da4547d70f8740ac2b4a5d82f88cebcd27f21bfe2",
+		shouldfail: false,
+	},
+	{
+		algorithms: []string{"pbkdf2", "pbkdf2$10000$50"},
+		password:   "abcdef",
+		salt:       "",
+		output:     "",
+		shouldfail: true,
+	},
+}
+
+// Ensure that the current code will correctly verify against the test vectors.
+func TestVectors(t *testing.T) {
+	for i, vector := range vectors {
+		for _, algorithm := range vector.algorithms {
+			t.Run(strconv.Itoa(i)+": "+algorithm, func(t *testing.T) {
+				pa := Parse(algorithm)
+				assert.Equal(t, !vector.shouldfail, pa.VerifyPassword(vector.password, vector.output, vector.salt))
+			})
+		}
+	}
+}
diff --git a/modules/auth/password/hash/pbkdf2.go b/modules/auth/password/hash/pbkdf2.go
new file mode 100644
index 0000000000..be3121318e
--- /dev/null
+++ b/modules/auth/password/hash/pbkdf2.go
@@ -0,0 +1,67 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"golang.org/x/crypto/pbkdf2"
+)
+
+func init() {
+	Register("pbkdf2", NewPBKDF2Hasher)
+}
+
+// PBKDF2Hasher implements PasswordHasher
+// and uses the PBKDF2 key derivation function.
+type PBKDF2Hasher struct {
+	iter, keyLen int
+}
+
+// HashWithSaltBytes a provided password and salt
+func (hasher *PBKDF2Hasher) HashWithSaltBytes(password string, salt []byte) string {
+	if hasher == nil {
+		return ""
+	}
+	return hex.EncodeToString(pbkdf2.Key([]byte(password), salt, hasher.iter, hasher.keyLen, sha256.New))
+}
+
+// NewPBKDF2Hasher is a factory method to create an PBKDF2Hasher
+// config should be either empty or of the form:
+// "<iter>$<keyLen>", where <x> is the string representation
+// of an integer
+func NewPBKDF2Hasher(config string) *PBKDF2Hasher {
+	// This default configuration uses the following parameters:
+	// iter=10000, keyLen=50.
+	// This matches the original configuration for `pbkdf2` prior to storing parameters
+	// in the database.
+	// THESE VALUES MUST NOT BE CHANGED OR BACKWARDS COMPATIBILITY WILL BREAK
+	hasher := &PBKDF2Hasher{
+		iter:   10_000,
+		keyLen: 50,
+	}
+
+	if config == "" {
+		return hasher
+	}
+
+	vals := strings.SplitN(config, "$", 2)
+	if len(vals) != 2 {
+		log.Error("invalid pbkdf2 hash spec %s", config)
+		return nil
+	}
+
+	var err error
+	hasher.iter, err = parseIntParam(vals[0], "iter", "pbkdf2", config, nil)
+	hasher.keyLen, err = parseIntParam(vals[1], "keyLen", "pbkdf2", config, err)
+	if err != nil {
+		return nil
+	}
+
+	return hasher
+}
diff --git a/modules/auth/password/hash/scrypt.go b/modules/auth/password/hash/scrypt.go
new file mode 100644
index 0000000000..e77434fc32
--- /dev/null
+++ b/modules/auth/password/hash/scrypt.go
@@ -0,0 +1,67 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"encoding/hex"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"golang.org/x/crypto/scrypt"
+)
+
+func init() {
+	Register("scrypt", NewScryptHasher)
+}
+
+// ScryptHasher implements PasswordHasher
+// and uses the scrypt key derivation function.
+type ScryptHasher struct {
+	n, r, p, keyLen int
+}
+
+// HashWithSaltBytes a provided password and salt
+func (hasher *ScryptHasher) HashWithSaltBytes(password string, salt []byte) string {
+	if hasher == nil {
+		return ""
+	}
+	hashedPassword, _ := scrypt.Key([]byte(password), salt, hasher.n, hasher.r, hasher.p, hasher.keyLen)
+	return hex.EncodeToString(hashedPassword)
+}
+
+// NewScryptHasher is a factory method to create an ScryptHasher
+// The provided config should be either empty or of the form:
+// "<n>$<r>$<p>$<keyLen>", where <x> is the string representation
+// of an integer
+func NewScryptHasher(config string) *ScryptHasher {
+	// This matches the original configuration for `scrypt` prior to storing hash parameters
+	// in the database.
+	// THESE VALUES MUST NOT BE CHANGED OR BACKWARDS COMPATIBILITY WILL BREAK
+	hasher := &ScryptHasher{
+		n:      1 << 16,
+		r:      16,
+		p:      2, // 2 passes through memory - this default config will use 128MiB in total.
+		keyLen: 50,
+	}
+
+	if config == "" {
+		return hasher
+	}
+
+	vals := strings.SplitN(config, "$", 4)
+	if len(vals) != 4 {
+		log.Error("invalid scrypt hash spec %s", config)
+		return nil
+	}
+	var err error
+	hasher.n, err = parseIntParam(vals[0], "n", "scrypt", config, nil)
+	hasher.r, err = parseIntParam(vals[1], "r", "scrypt", config, err)
+	hasher.p, err = parseIntParam(vals[2], "p", "scrypt", config, err)
+	hasher.keyLen, err = parseIntParam(vals[3], "keyLen", "scrypt", config, err)
+	if err != nil {
+		return nil
+	}
+	return hasher
+}
diff --git a/modules/auth/password/hash/setting.go b/modules/auth/password/hash/setting.go
new file mode 100644
index 0000000000..7016974304
--- /dev/null
+++ b/modules/auth/password/hash/setting.go
@@ -0,0 +1,61 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+// DefaultHashAlgorithmName represents the default value of PASSWORD_HASH_ALGO
+// configured in app.ini.
+//
+// It is NOT the same and does NOT map to the defaultEmptyHashAlgorithmSpecification.
+//
+// It will be dealiased as per aliasAlgorithmNames whereas
+// defaultEmptyHashAlgorithmSpecification does not undergo dealiasing.
+const DefaultHashAlgorithmName = "pbkdf2"
+
+var DefaultHashAlgorithm *PasswordHashAlgorithm
+
+// aliasAlgorithNames provides a mapping between the value of PASSWORD_HASH_ALGO
+// configured in the app.ini and the parameters used within the hashers internally.
+//
+// If it is necessary to change the default parameters for any hasher in future you
+// should change these values and not those in argon2.go etc.
+var aliasAlgorithmNames = map[string]string{
+	"argon2":    "argon2$2$65536$8$50",
+	"bcrypt":    "bcrypt$10",
+	"scrypt":    "scrypt$65536$16$2$50",
+	"pbkdf2":    "pbkdf2_v2", // pbkdf2 should default to pbkdf2_v2
+	"pbkdf2_v1": "pbkdf2$10000$50",
+	// The latest PBKDF2 password algorithm is used as the default since it doesn't
+	// use a lot of  memory and is safer to use on less powerful devices.
+	"pbkdf2_v2": "pbkdf2$50000$50",
+	// The pbkdf2_hi password algorithm is offered as a stronger alternative to the
+	// slightly improved pbkdf2_v2 algorithm
+	"pbkdf2_hi": "pbkdf2$320000$50",
+}
+
+var RecommendedHashAlgorithms = []string{
+	"pbkdf2",
+	"argon2",
+	"bcrypt",
+	"scrypt",
+	"pbkdf2_hi",
+}
+
+// SetDefaultPasswordHashAlgorithm will take a provided algorithmName and dealias it to
+// a complete algorithm specification.
+func SetDefaultPasswordHashAlgorithm(algorithmName string) (string, *PasswordHashAlgorithm) {
+	if algorithmName == "" {
+		algorithmName = DefaultHashAlgorithmName
+	}
+	alias, has := aliasAlgorithmNames[algorithmName]
+	for has {
+		algorithmName = alias
+		alias, has = aliasAlgorithmNames[algorithmName]
+	}
+
+	// algorithmName should now be a full algorithm specification
+	// e.g. pbkdf2$50000$50 rather than pbdkf2
+	DefaultHashAlgorithm = Parse(algorithmName)
+
+	return algorithmName, DefaultHashAlgorithm
+}
diff --git a/modules/auth/password/hash/setting_test.go b/modules/auth/password/hash/setting_test.go
new file mode 100644
index 0000000000..d707207db6
--- /dev/null
+++ b/modules/auth/password/hash/setting_test.go
@@ -0,0 +1,38 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCheckSettingPasswordHashAlgorithm(t *testing.T) {
+	t.Run("pbkdf2 is pbkdf2_v2", func(t *testing.T) {
+		pbkdf2v2Config, pbkdf2v2Algo := SetDefaultPasswordHashAlgorithm("pbkdf2_v2")
+		pbkdf2Config, pbkdf2Algo := SetDefaultPasswordHashAlgorithm("pbkdf2")
+
+		assert.Equal(t, pbkdf2v2Config, pbkdf2Config)
+		assert.Equal(t, pbkdf2v2Algo.Specification, pbkdf2Algo.Specification)
+	})
+
+	for a, b := range aliasAlgorithmNames {
+		t.Run(a+"="+b, func(t *testing.T) {
+			aConfig, aAlgo := SetDefaultPasswordHashAlgorithm(a)
+			bConfig, bAlgo := SetDefaultPasswordHashAlgorithm(b)
+
+			assert.Equal(t, bConfig, aConfig)
+			assert.Equal(t, aAlgo.Specification, bAlgo.Specification)
+		})
+	}
+
+	t.Run("pbkdf2_v2 is the default when default password hash algorithm is empty", func(t *testing.T) {
+		emptyConfig, emptyAlgo := SetDefaultPasswordHashAlgorithm("")
+		pbkdf2v2Config, pbkdf2v2Algo := SetDefaultPasswordHashAlgorithm("pbkdf2_v2")
+
+		assert.Equal(t, pbkdf2v2Config, emptyConfig)
+		assert.Equal(t, pbkdf2v2Algo.Specification, emptyAlgo.Specification)
+	})
+}
diff --git a/modules/password/password.go b/modules/auth/password/password.go
index fe2a2a7bd5..2172dc8b44 100644
--- a/modules/password/password.go
+++ b/modules/auth/password/password.go
@@ -11,8 +11,8 @@ import (
 	"strings"
 	"sync"
 
-	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/translation"
 )
 
 // complexity contains information about a particular kind of password complexity
@@ -112,13 +112,13 @@ func Generate(n int) (string, error) {
 }
 
 // BuildComplexityError builds the error message when password complexity checks fail
-func BuildComplexityError(ctx *context.Context) string {
+func BuildComplexityError(locale translation.Locale) string {
 	var buffer bytes.Buffer
-	buffer.WriteString(ctx.Tr("form.password_complexity"))
+	buffer.WriteString(locale.Tr("form.password_complexity"))
 	buffer.WriteString("<ul>")
 	for _, c := range requiredList {
 		buffer.WriteString("<li>")
-		buffer.WriteString(ctx.Tr(c.TrNameOne))
+		buffer.WriteString(locale.Tr(c.TrNameOne))
 		buffer.WriteString("</li>")
 	}
 	buffer.WriteString("</ul>")
diff --git a/modules/password/password_test.go b/modules/auth/password/password_test.go
index 6c35dc86bd..6c35dc86bd 100644
--- a/modules/password/password_test.go
+++ b/modules/auth/password/password_test.go
diff --git a/modules/password/pwn.go b/modules/auth/password/pwn.go
index 91bad0d25b..df425ac659 100644
--- a/modules/password/pwn.go
+++ b/modules/auth/password/pwn.go
@@ -6,7 +6,7 @@ package password
 import (
 	"context"
 
-	"code.gitea.io/gitea/modules/password/pwn"
+	"code.gitea.io/gitea/modules/auth/password/pwn"
 	"code.gitea.io/gitea/modules/setting"
 )
 
diff --git a/modules/password/pwn/pwn.go b/modules/auth/password/pwn/pwn.go
index b5a015fb9c..b5a015fb9c 100644
--- a/modules/password/pwn/pwn.go
+++ b/modules/auth/password/pwn/pwn.go
diff --git a/modules/password/pwn/pwn_test.go b/modules/auth/password/pwn/pwn_test.go
index 148208b964..148208b964 100644
--- a/modules/password/pwn/pwn_test.go
+++ b/modules/auth/password/pwn/pwn_test.go
diff --git a/modules/setting/setting.go b/modules/setting/setting.go
index a68a46f7ad..0cd2db356d 100644
--- a/modules/setting/setting.go
+++ b/modules/setting/setting.go
@@ -21,6 +21,7 @@ import (
 	"text/template"
 	"time"
 
+	"code.gitea.io/gitea/modules/auth/password/hash"
 	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/generate"
 	"code.gitea.io/gitea/modules/json"
@@ -968,7 +969,14 @@ func loadFromConf(allowEmpty bool, extraConfig string) {
 	DisableGitHooks = sec.Key("DISABLE_GIT_HOOKS").MustBool(true)
 	DisableWebhooks = sec.Key("DISABLE_WEBHOOKS").MustBool(false)
 	OnlyAllowPushIfGiteaEnvironmentSet = sec.Key("ONLY_ALLOW_PUSH_IF_GITEA_ENVIRONMENT_SET").MustBool(true)
-	PasswordHashAlgo = sec.Key("PASSWORD_HASH_ALGO").MustString("pbkdf2")
+
+	// Ensure that the provided default hash algorithm is a valid hash algorithm
+	var algorithm *hash.PasswordHashAlgorithm
+	PasswordHashAlgo, algorithm = hash.SetDefaultPasswordHashAlgorithm(sec.Key("PASSWORD_HASH_ALGO").MustString(""))
+	if algorithm == nil {
+		log.Fatal("The provided password hash algorithm was invalid: %s", sec.Key("PASSWORD_HASH_ALGO").MustString(""))
+	}
+
 	CSRFCookieHTTPOnly = sec.Key("CSRF_COOKIE_HTTP_ONLY").MustBool(true)
 	PasswordCheckPwn = sec.Key("PASSWORD_CHECK_PWN").MustBool(false)
 	SuccessfulTokensCacheSize = sec.Key("SUCCESSFUL_TOKENS_CACHE_SIZE").MustInt(20)