Implement NIP-44 decrypt

nip44.go

@@ -1,6 +1,7 @@
 package nip44
 
 import (
+	"bytes"
 	"crypto/hmac"
 	"crypto/rand"
 	"crypto/sha256"
@@ -47,7 +48,7 @@ func Encrypt(key []byte, plaintext string, options *EncryptOptions) (string, err
 		}
 	}
 	if version != 2 {
-		return "", errors.New("unknown encryption version")
+		return "", errors.New("unknown version")
 	}
 	if len(salt) != 32 {
 		return "", errors.New("salt must be 32 bytes")
@@ -69,6 +70,50 @@ func Encrypt(key []byte, plaintext string, options *EncryptOptions) (string, err
 	return base64.StdEncoding.EncodeToString(concat), nil
 }
 
+func Decrypt(key []byte, ciphertext string) (string, error) {
+	var (
+		version     int = 2
+		decoded     []byte
+		dLen        int
+		salt        []byte
+		ciphertext_ []byte
+		hmac_       []byte
+		enc         []byte
+		nonce       []byte
+		auth        []byte
+		padded      []byte
+		unpaddedLen uint16
+		unpadded    []byte
+		err         error
+	)
+	if ciphertext[0:1] == "#" {
+		return "", errors.New("unknown version")
+	}
+	if decoded, err = base64.StdEncoding.DecodeString(ciphertext); err != nil {
+		return "", err
+	}
+	if version = int(decoded[0]); version != 2 {
+		return "", errors.New("unknown version")
+	}
+	dLen = len(decoded)
+	salt, ciphertext_, hmac_ = decoded[1:33], decoded[33:dLen-32], decoded[dLen-32:]
+	if enc, nonce, auth, err = messageKeys(key, salt); err != nil {
+		return "", err
+	}
+	if !bytes.Equal(hmac_, sha256Hmac(auth, ciphertext_)) {
+		return "", errors.New("invalid hmac")
+	}
+	if padded, err = chacha20Encrypt(enc, nonce, ciphertext_); err != nil {
+		return "", err
+	}
+	unpaddedLen = binary.BigEndian.Uint16(padded[0:2])
+	unpadded = padded[2 : unpaddedLen+2]
+	if len(unpadded) == 0 || len(unpadded) != int(unpaddedLen) || len(padded) != 2+calcPadding(int(unpaddedLen)) {
+		return "", errors.New("invalid padding")
+	}
+	return string(unpadded), nil
+}
+
 func chacha20Encrypt(key []byte, nonce []byte, message []byte) ([]byte, error) {
 	var (
 		cipher *chacha20.Cipher

nip44_test.go

@@ -8,11 +8,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func assertEncrypt(t *testing.T, key string, salt string, plaintext string, expected string) {
+func assertCrypt(t *testing.T, key string, salt string, plaintext string, expected string) {
 	var (
 		k         []byte
 		s         []byte
 		actual    string
+		decrypted string
 		err       error
 	)
 	if k, err = hex.DecodeString(key); err != nil {
@@ -24,11 +25,15 @@ func assertEncrypt(t *testing.T, key string, salt string, plaintext string, expe
 	actual, err = nip44.Encrypt(k, plaintext, &nip44.EncryptOptions{Salt: s})
 	if assert.NoError(t, err) {
 		assert.Equal(t, expected, actual)
+		decrypted, err = nip44.Decrypt(k, expected)
+		if assert.NoError(t, err) {
+			assert.Equal(t, decrypted, plaintext)
+		}
 	}
 }
 
-func TestEncrypt001(t *testing.T) {
+func TestCrypt001(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5",
 		"0000000000000000000000000000000000000000000000000000000000000001",
 		"a",
@@ -36,8 +41,8 @@ func TestEncrypt001(t *testing.T) {
 	)
 }
 
-func TestEncrypt002(t *testing.T) {
+func TestCrypt002(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5",
 		"f00000000000000000000000000000f00000000000000000000000000000000f",
 		"🍕🫃",
@@ -45,8 +50,8 @@ func TestEncrypt002(t *testing.T) {
 	)
 }
 
-func TestEncrypt003(t *testing.T) {
+func TestCrypt003(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"94da47d851b9c1ed33b3b72f35434f56aa608d60e573e9c295f568011f4f50a4",
 		"b635236c42db20f021bb8d1cdff5ca75dd1a0cc72ea742ad750f33010b24f73b",
 		"表ポあA鷗ŒéＢ逍Üߪąñ丂㐀𠀀",
@@ -54,8 +59,8 @@ func TestEncrypt003(t *testing.T) {
 	)
 }
 
-func TestEncrypt004(t *testing.T) {
+func TestCrypt004(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"ab99c122d4586cdd5c813058aa543d0e7233545dbf6874fc34a3d8d9a18fbbc3",
 		"b20989adc3ddc41cd2c435952c0d59a91315d8c5218d5040573fc3749543acaf",
 		"ability🤝的 ȺȾ",
@@ -63,8 +68,8 @@ func TestEncrypt004(t *testing.T) {
 	)
 }
 
-func TestEncrypt005(t *testing.T) {
+func TestCrypt005(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"a449f2a85c6d3db0f44c64554a05d11a3c0988d645e4b4b2592072f63662f422",
 		"8d4442713eb9d4791175cb040d98d6fc5be8864d6ec2f89cf0895a2b2b72d1b1",
 		"pepper👀їжак",
@@ -72,8 +77,8 @@ func TestEncrypt005(t *testing.T) {
 	)
 }
 
-func TestEncrypt006(t *testing.T) {
+func TestCrypt006(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"decde9938ffcb14fa7ff300105eb1bf239469af9baf376e69755b9070ae48c47",
 		"2180b52ae645fcf9f5080d81b1f0b5d6f2cd77ff3c986882bb549158462f3407",
 		"( ͡° ͜ʖ ͡°)",
@@ -81,8 +86,8 @@ func TestEncrypt006(t *testing.T) {
 	)
 }
 
-func TestEncrypt007(t *testing.T) {
+func TestCrypt007(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6f2fde7aa00208c388f506455c31c3fa07caf8b516d43bf7514ee19edcda994",
 		"e4cd5f7ce4eea024bc71b17ad456a986a74ac426c2c62b0a15eb5c5c8f888b68",
 		"مُنَاقَشَةُ سُبُلِ اِسْتِخْدَامِ اللُّغَةِ فِي النُّظُمِ الْقَائِمَةِ وَفِيم يَخُصَّ التَّطْبِيقَاتُ الْحاسُوبِيَّةُ،",
@@ -90,8 +95,8 @@ func TestEncrypt007(t *testing.T) {
 	)
 }
 
-func TestEncrypt008(t *testing.T) {
+func TestCrypt008(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6f2fde7aa00208c388f506455c31c3fa07caf8b516d43bf7514ee19edcda994",
 		"38d1ca0abef9e5f564e89761a86cee04574b6825d3ef2063b10ad75899e4b023",
 		"الكل في المجمو عة (5)",
@@ -99,8 +104,8 @@ func TestEncrypt008(t *testing.T) {
 	)
 }
 
-func TestEncrypt009(t *testing.T) {
+func TestCrypt009(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6f2fde7aa00208c388f506455c31c3fa07caf8b516d43bf7514ee19edcda994",
 		"4f1a31909f3483a9e69c8549a55bbc9af25fa5bbecf7bd32d9896f83ef2e12e0",
 		"𝖑𝖆𝖟𝖞 社會科學院語學研究所",
@@ -108,8 +113,8 @@ func TestEncrypt009(t *testing.T) {
 	)
 }
 
-func TestEncrypt010(t *testing.T) {
+func TestCrypt010(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"c6f2fde7aa00208c388f506455c31c3fa07caf8b516d43bf7514ee19edcda994",
 		"a3e219242d85465e70adcd640b564b3feff57d2ef8745d5e7a0663b2dccceb54",
 		"🙈 🙉 🙊 0️⃣ 1️⃣ 2️⃣ 3️⃣ 4️⃣ 5️⃣ 6️⃣ 7️⃣ 8️⃣ 9️⃣ 🔟 Powerلُلُصّبُلُلصّبُررً ॣ ॣh ॣ ॣ冗",
@@ -117,24 +122,24 @@ func TestEncrypt010(t *testing.T) {
 	)
 }
 
-func TestEncrypt011(t *testing.T) {
+func TestCrypt011(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"7a1ccf5ce5a08e380f590de0c02776623b85a61ae67cfb6a017317e505b7cb51",
 		"a000000000000000000000000000000000000000000000000000000000000001",
 		"⁰⁴⁵₀₁₂",
 		"AqAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAB2+xmGnjIMPMqqJGmjdYAYZUDUyEEUO3/evHUaO40LePeR91VlMVZ7I+nKJPkaUiKZ3cQiQnA86Uwti2IxepmzOFN",
 	)
 }
-func TestEncrypt012(t *testing.T) {
+func TestCrypt012(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"aa971537d741089885a0b48f2730a125e15b36033d089d4537a4e1204e76b39e",
 		"b000000000000000000000000000000000000000000000000000000000000002",
 		"A Peer-to-Peer Electronic Cash System",
 		"ArAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACyuqG6RycuPyDPtwxzTcuMQu+is3N5XuWTlvCjligVaVBRydexaylXbsX592MEd3/Jt13BNL/GlpYpGDvLS4Tt/+2s9FX/16e/RDc+czdwXglc4DdSHiq+O06BvvXYfEQOPw=",
 	)
 }
-func TestEncrypt013(t *testing.T) {
+func TestCrypt013(t *testing.T) {
-	assertEncrypt(t,
+	assertCrypt(t,
 		"79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798",
 		"79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798",
 		"A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution. Digital signatures provide part of the solution, but the main benefits are lost if a trusted third party is still required to prevent double-spending.",