cfca: extract encrypt/decrypt functions with SM4CBC and SM3 KDF

cfca/encrypt.go

@@ -0,0 +1,57 @@
+// Copyright 2024 Sun Yimin. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package cfca
+
+import (
+	"crypto/cipher"
+	"errors"
+
+	"github.com/emmansun/gmsm/padding"
+	"github.com/emmansun/gmsm/sm3"
+	"github.com/emmansun/gmsm/sm4"
+)
+
+// NewSM4CBCBlockMode creates a new SM4-CBC block mode with the password.
+func NewSM4CBCBlockMode(password []byte, isEncrypter bool) (cipher.BlockMode, error) {
+	if len(password) == 0 {
+		return nil, errors.New("cfca: invalid password")
+	}
+	ivkey := sm3.Kdf(password, 32)
+	block, err := sm4.NewCipher(ivkey[16:])
+	if err != nil {
+		return nil, err
+	}
+	if isEncrypter {
+		return cipher.NewCBCEncrypter(block, ivkey[:16]), nil
+	}
+	return cipher.NewCBCDecrypter(block, ivkey[:16]), nil
+}
+
+// EncryptBySM4CBC encrypts the data with the password using SM4-CBC algorithm.
+// Corresponds to the cfca.sadk.util.encryptMessageBySM4 method.
+func EncryptBySM4CBC(plaintext, password []byte) ([]byte, error) {
+	mode, err := NewSM4CBCBlockMode(password, true)
+	if err != nil {
+		return nil, err
+	}
+	pkcs7 := padding.NewPKCS7Padding(uint(mode.BlockSize()))
+	plaintext = pkcs7.Pad(plaintext)
+	ciphertext := make([]byte, len(plaintext))
+	mode.CryptBlocks(ciphertext, plaintext)
+	return ciphertext, nil
+}
+
+// DecryptBySM4CBC decrypts the data with the password using SM4-CBC algorithm.
+// Corresponds to the cfca.sadk.util.decryptMessageBySM4 method.
+func DecryptBySM4CBC(ciphertext, password []byte) ([]byte, error) {
+	mode, err := NewSM4CBCBlockMode(password, false)
+	if err != nil {
+		return nil, err
+	}
+	plaintext := make([]byte, len(ciphertext))
+	mode.CryptBlocks(plaintext, ciphertext)
+	pkcs7 := padding.NewPKCS7Padding(uint(mode.BlockSize()))
+	return pkcs7.Unpad(plaintext)
+}

cfca/pkcs12_sm2.go

@@ -2,18 +2,14 @@
 package cfca
 
 import (
-	"crypto/cipher"
 	"encoding/asn1"
 	"errors"
 	"fmt"
 	"math/big"
 
-	"github.com/emmansun/gmsm/padding"
 	"github.com/emmansun/gmsm/pkcs"
 	"github.com/emmansun/gmsm/pkcs7"
 	"github.com/emmansun/gmsm/sm2"
-	"github.com/emmansun/gmsm/sm3"
-	"github.com/emmansun/gmsm/sm4"
 	"github.com/emmansun/gmsm/smx509"
 )
 
@@ -59,18 +55,11 @@ func ParseSM2(password, data []byte) (*sm2.PrivateKey, *smx509.Certificate, erro
 	if !keys.EncryptedKey.Algorithm.Equal(oidSM4) && !keys.EncryptedKey.Algorithm.Equal(oidSM4CBC) {
 		return nil, nil, fmt.Errorf("cfca: unsupported algorithm <%v>", keys.EncryptedKey.Algorithm)
 	}
-	ivkey := sm3.Kdf(password, 32)
-	marshalledIV, err := asn1.Marshal(ivkey[:16])
+	pk, err := DecryptBySM4CBC(keys.EncryptedKey.EncryptedContent.Bytes, password)
 	if err != nil {
 		return nil, nil, err
 	}
-	pk, err := pkcs.SM4CBC.Decrypt(ivkey[16:], &asn1.RawValue{FullBytes: marshalledIV}, keys.EncryptedKey.EncryptedContent.Bytes)
-	if err != nil {
-		return nil, nil, err
-	}
-	d := new(big.Int).SetBytes(pk) // here we do NOT check if the d is in (0, N) or not
-	// Create private key from *big.Int
-	prvKey, err := sm2.NewPrivateKeyFromInt(d)
+	prvKey, err := sm2.NewPrivateKeyFromInt(new(big.Int).SetBytes(pk))
 	if err != nil {
 		return nil, nil, err
 	}
@@ -87,22 +76,12 @@ func ParseSM2(password, data []byte) (*sm2.PrivateKey, *smx509.Certificate, erro
 
 // MarshalSM2 encodes sm2 private key and related certificate to cfca defined format
 func MarshalSM2(password []byte, key *sm2.PrivateKey, cert *smx509.Certificate) ([]byte, error) {
-	if len(password) == 0 {
-		return nil, errors.New("cfca: invalid password")
-	}
-	ivkey := sm3.Kdf(password, 32)
-	block, err := sm4.NewCipher(ivkey[16:])
-	if err != nil {
+	var err error
+	var ciphertext []byte
+	if ciphertext, err = EncryptBySM4CBC(key.D.Bytes(), password); err != nil {
 		return nil, err
 	}
-	mode := cipher.NewCBCEncrypter(block, ivkey[:16])
-	pkcs7 := padding.NewPKCS7Padding(uint(block.BlockSize()))
-	plainText := pkcs7.Pad(key.D.Bytes())
-	ciphertext := make([]byte, len(plainText))
-	mode.CryptBlocks(ciphertext, plainText)
-
-	ciphertext, err = asn1.Marshal(ciphertext)
-	if err != nil {
+	if ciphertext, err = asn1.Marshal(ciphertext); err != nil {
 		return nil, err
 	}
 

docs/cfca.md

@@ -100,8 +100,9 @@ SADK 3.2之后的版本，支持下列SM2密文格式(encryptedType)：
 * 0x04 - C1为非压缩点格式，具体是C1C3C2还是C1C2C3取决于解密时的选项参数，默认为C1C3C2。
 * 0x02/0x03 - C1为压缩点格式，具体是C1C3C2还是C1C2C3取决于解密时的选项参数，默认为C1C3C2。
 
+### 生成双密钥CSR （v0.29.6+）
+`cfca.CreateCertificateRequest`，和CFCA SADK不同，调用者需要自行先生成两对密钥对，一对用于签名证书，一对用于加解密CFCA生成的加密用私钥文件（CFCA加密，申请者解密）。
+使用`cfca.ParseEscrowPrivateKey`解析CFCA返回的加密用私钥。
+
 ### SM2私钥、证书的解析
 这个是CFCA自定义的，未见相关标准，可以通过```cfca.ParseSM2```来解析。
-
-### 生成双密钥CSR
-`cfca.CreateCertificateRequest`，和CFCA SADK不同，调用者需要自行先生成两对密钥对，一对用于签名证书，一对用于加解密CFCA生成的加密用私钥文件（CFCA加密，申请者解密）。