1 files changed, 189 insertions, 0 deletions
diff --git a/modules/auth/password/hash/hash.go b/modules/auth/password/hash/hash.go
new file mode 100644
index 0000000..459320e
--- /dev/null
+++ b/modules/auth/password/hash/hash.go
@@ -0,0 +1,189 @@
+// 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{}
+)
+
+// MustRegister registers a PasswordSaltHasher with the availableHasherFactories
+// Caution: This is not thread safe.
+func MustRegister[T PasswordSaltHasher](name string, newFn func(config string) T) {
+	if err := Register(name, newFn); err != nil {
+		panic(err)
+	}
+}
+
+// Register registers a PasswordSaltHasher with the availableHasherFactories
+// Caution: This is not thread safe.
+func Register[T PasswordSaltHasher](name string, newFn func(config string) T) error {
+	if _, has := availableHasherFactories[name]; has {
+		return fmt.Errorf("duplicate registration of password salt hasher: %s", name)
+	}
+
+	availableHasherFactories[name] = func(config string) PasswordSaltHasher {
+		n := newFn(config)
+		return n
+	}
+	return nil
+}
+
+// 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
+}