authkit initial

hasher/argon2id.go

@@ -0,0 +1,136 @@
+// Package hasher provides authkit.Hasher implementations. The default
+// implementation, Argon2id, encodes hashes in the standard PHC string format
+// (https://github.com/P-H-C/phc-string-format) so callers can introspect
+// parameters and migrate.
+package hasher
+
+import (
+	"crypto/rand"
+	"crypto/subtle"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+
+	"git.juancwu.dev/juancwu/authkit"
+	"git.juancwu.dev/juancwu/errx"
+	"golang.org/x/crypto/argon2"
+)
+
+// Argon2idParams configures the Argon2id KDF.
+type Argon2idParams struct {
+	Memory      uint32 // KB; OWASP 2024 baseline: 19 MiB minimum, 64 MiB recommended
+	Iterations  uint32 // time cost
+	Parallelism uint8  // lanes
+	SaltLen     uint32 // bytes
+	KeyLen      uint32 // bytes
+}
+
+// DefaultArgon2idParams returns sensible defaults: 64 MiB memory, 3
+// iterations, 2 lanes, 16-byte salt, 32-byte key. Tune up Memory/Iterations
+// over time and rely on Verify's needsRehash signal to migrate stored hashes.
+func DefaultArgon2idParams() Argon2idParams {
+	return Argon2idParams{
+		Memory:      64 * 1024,
+		Iterations:  3,
+		Parallelism: 2,
+		SaltLen:     16,
+		KeyLen:      32,
+	}
+}
+
+type argon2idHasher struct {
+	params Argon2idParams
+	rng    io.Reader
+}
+
+// NewArgon2id builds an authkit.Hasher backed by Argon2id. If params is the
+// zero value, DefaultArgon2idParams() is used. rng defaults to crypto/rand.
+func NewArgon2id(params Argon2idParams, rng io.Reader) authkit.Hasher {
+	if params == (Argon2idParams{}) {
+		params = DefaultArgon2idParams()
+	}
+	if rng == nil {
+		rng = rand.Reader
+	}
+	return &argon2idHasher{params: params, rng: rng}
+}
+
+func (h *argon2idHasher) Hash(password string) (string, error) {
+	const op = "authkit.hasher.Argon2id.Hash"
+	if password == "" {
+		return "", errx.New(op, "password is empty")
+	}
+	salt := make([]byte, h.params.SaltLen)
+	if _, err := io.ReadFull(h.rng, salt); err != nil {
+		return "", errx.Wrap(op, err)
+	}
+	key := argon2.IDKey([]byte(password), salt,
+		h.params.Iterations, h.params.Memory, h.params.Parallelism, h.params.KeyLen)
+	return encodePHC(h.params, salt, key), nil
+}
+
+func (h *argon2idHasher) Verify(password, encoded string) (bool, bool, error) {
+	const op = "authkit.hasher.Argon2id.Verify"
+	got, salt, key, err := decodePHC(encoded)
+	if err != nil {
+		return false, false, errx.Wrap(op, err)
+	}
+	want := argon2.IDKey([]byte(password), salt,
+		got.Iterations, got.Memory, got.Parallelism, uint32(len(key)))
+	if subtle.ConstantTimeCompare(want, key) != 1 {
+		return false, false, nil
+	}
+	needsRehash := got.Memory != h.params.Memory ||
+		got.Iterations != h.params.Iterations ||
+		got.Parallelism != h.params.Parallelism ||
+		uint32(len(salt)) != h.params.SaltLen ||
+		uint32(len(key)) != h.params.KeyLen
+	return true, needsRehash, nil
+}
+
+// PHC string format:
+//
+//	$argon2id$v=19$m=<mem>,t=<iters>,p=<lanes>$<salt b64>$<key b64>
+//
+// base64 here is the unpadded standard alphabet, per the spec.
+func encodePHC(p Argon2idParams, salt, key []byte) string {
+	enc := base64.RawStdEncoding
+	return fmt.Sprintf(
+		"$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
+		argon2.Version, p.Memory, p.Iterations, p.Parallelism,
+		enc.EncodeToString(salt), enc.EncodeToString(key),
+	)
+}
+
+func decodePHC(s string) (Argon2idParams, []byte, []byte, error) {
+	parts := strings.Split(s, "$")
+	// Expect: ["", "argon2id", "v=19", "m=...,t=...,p=...", "<salt>", "<key>"]
+	if len(parts) != 6 || parts[0] != "" || parts[1] != "argon2id" {
+		return Argon2idParams{}, nil, nil, errors.New("hasher: not an argon2id phc string")
+	}
+	var version int
+	if _, err := fmt.Sscanf(parts[2], "v=%d", &version); err != nil {
+		return Argon2idParams{}, nil, nil, fmt.Errorf("hasher: bad version segment: %w", err)
+	}
+	if version != argon2.Version {
+		return Argon2idParams{}, nil, nil, fmt.Errorf("hasher: unsupported argon2 version %d", version)
+	}
+	var p Argon2idParams
+	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &p.Memory, &p.Iterations, &p.Parallelism); err != nil {
+		return Argon2idParams{}, nil, nil, fmt.Errorf("hasher: bad params segment: %w", err)
+	}
+	enc := base64.RawStdEncoding
+	salt, err := enc.DecodeString(parts[4])
+	if err != nil {
+		return Argon2idParams{}, nil, nil, fmt.Errorf("hasher: bad salt: %w", err)
+	}
+	key, err := enc.DecodeString(parts[5])
+	if err != nil {
+		return Argon2idParams{}, nil, nil, fmt.Errorf("hasher: bad key: %w", err)
+	}
+	p.SaltLen = uint32(len(salt))
+	p.KeyLen = uint32(len(key))
+	return p, salt, key, nil
+}