pkcs7: update comments and document

docs/pkcs7.md

@@ -40,18 +40,25 @@
 ### 签名数据（Signed Data）
 签名数据，使用证书对应的私钥进行签名，理论上支持多个签名者，但通常使用场景都是单签。和数字信封数据类似，也分国密和非国密。
 
-#### 创建签名数据
+#### 签名流程
+1. 创建SignedData
 （是否国密是指OID也使用国密体系）
 
-| 是否国密 | 方法 | 默认签名算法 |    
-| :--- | :--- | :--- |
-| 否 | ```NewSignedData``` | SHA1 |  
-| 是 | ```NewSMSignedData``` | SM3 |  
+| 是否国密 | 数据是否是哈希值 | 方法 | 默认签名算法 |    
+| :--- | :--- | :--- | :--- |
+| 否 | 否 | ```NewSignedData``` | SHA1 |  
+| 否 | 是 | ```NewSignedDataWithDigest``` | SHA1 |  
+| 是 | 否 | ```NewSMSignedData``` | SM3 |  
+| 是 | 是 | ```NewSMSignedDataWithDigest``` | SM3 |  
 
-可选步骤：调用```SetDigestAlgorithm```设置想要的签名算法，通常国密不需要修改。    
-接着调用```AddSigner```或```AddSignerChain```方法，进行签名；可以通过```SignerInfoConfig.SkipCertificates```指定忽略证书项（最终签名数据中不包含证书项）；  
-如果进行Detach签名，则调用```Detach```方法；  
-最后调用```Finish```方法，序列化输出结果。  
+2. 可选步骤：调用```SetDigestAlgorithm```设置想要的签名算法，通常国密**不需要**修改。    
+3. 接着调用```AddSigner```或```AddSignerChain```方法，进行签名；可以通过```SignerInfoConfig.SkipCertificates```指定忽略证书项（最终签名数据中不包含证书项）；  
+4. 如果进行Detach签名，则调用```Detach```方法；  
+5. 最后调用```Finish```方法，序列化输出结果。  
+
+**注意**：
+1. 如果是直接对哈希值签名，一定是Detach签名。
+2. 国密签名如果要传入哈希值，在有Attribute的情况下，则哈希值只是标准的SM3哈希值；否则必须是符合SM2签名标准的哈希值（含SM2公钥信息）。
 
 #### Detach签名
 就是外部签名，**被签名数据**不包含在SignedData中（也就是其ContentInfo.Content为空）。
@@ -86,7 +93,7 @@ if err := p7.VerifyWithChain(truststore); err != nil {
 1. 调用```Parse```方法；
 2. 如果是Detach签名数据，则手动设置原始数据（参考```testSign```方法）；
 3. 如果签名数据中不包含证书项，则手动设置验签证书（参考```TestSkipCertificates```）；
-4. 调用```Verify```或```VerifyWithChain```方法。
+4. 如果Content是原始数据，调用```Verify```或```VerifyWithChain```方法；如果Content是哈希值，调用```VerifyAsDigest```或```VerifyAsDigestWithChain```方法。
 
 #### 特殊方法
 ```DegenerateCertificate```，退化成签名数据中只包含证书，目前没有使用SM2 OID的方法，如果需要可以请求添加。可以参考```TestDegenerateCertificate```和```TestParseSM2CertificateChain```。

pkcs7/sign.go

@@ -48,9 +48,9 @@ func NewSignedData(data []byte) (*SignedData, error) {
 	return &SignedData{sd: sd, data: data, digestOid: OIDDigestAlgorithmSHA1, contentTypeOid: OIDSignedData}, nil
 }
 
-// NewSignedDataWithDigest creates a new SignedData instance using the provided digest.
-// It sets the isDigest field to true, indicating that the input is already a digest.
-// Returns the SignedData instance or an error if the creation fails.
+// NewSignedDataWithDigest creates a new SignedData structure with the provided digest.
+// The digest is used to initialize the SignedData object, and the content is set to an empty ASN.1 RawValue.
+// The function returns a pointer to the SignedData object and an error if any occurs.
 func NewSignedDataWithDigest(digest []byte) (*SignedData, error) {
 	ci := contentInfo{
 		ContentType: OIDData,
@@ -64,9 +64,10 @@ func NewSignedDataWithDigest(digest []byte) (*SignedData, error) {
 	return &SignedData{sd: sd, data: digest, digestOid: OIDDigestAlgorithmSHA1, contentTypeOid: OIDSignedData, isDigestProvided: true}, nil
 }
 
-// NewSMSignedData takes data and initializes a PKCS7 SignedData struct that is
-// ready to be signed via AddSigner. The digest algorithm is set to SM3 by default
-// and can be changed by calling SetDigestAlgorithm.
+// NewSMSignedData creates a new SignedData object using the provided data
+// and sets the appropriate OIDs for SM2 and SM3 algorithms.
+// It returns a pointer to the SignedData object and an error if any occurs
+// during the creation of the SignedData object.
 func NewSMSignedData(data []byte) (*SignedData, error) {
 	sd, err := NewSignedData(data)
 	if err != nil {
@@ -78,25 +79,28 @@ func NewSMSignedData(data []byte) (*SignedData, error) {
 	return sd, nil
 }
 
-// NewSMSignedDataWithDigest creates a new SignedData object using the provided digest.
-// It calls the NewSMSignedData function with the given digest and sets the isDigest flag to true.
-// If there is an error during the creation of the SignedData object, it returns the error.
+// NewSMSignedDataWithDigest creates a new SignedData structure with the provided digest.
+// The digest is expected to be a precomputed hash of the content to be signed.
+// This function initializes the SignedData with the necessary OIDs for SM3 and SM2 algorithms.
 func NewSMSignedDataWithDigest(digest []byte) (*SignedData, error) {
-	sd, err := NewSignedDataWithDigest(digest)
-	if err != nil {
-		return nil, err
+	ci := contentInfo{
+		ContentType: SM2OIDData,
+		Content:     asn1.RawValue{}, // for sign digest, content is empty
 	}
-	sd.sd.ContentInfo.ContentType = SM2OIDData
-	sd.digestOid = OIDDigestAlgorithmSM3
-	sd.contentTypeOid = SM2OIDSignedData
-	return sd, nil
+	sd := signedData{
+		ContentInfo: ci,
+		Version:     1,
+	}
+	return &SignedData{sd: sd, data: digest, digestOid: OIDDigestAlgorithmSM3, contentTypeOid: SM2OIDSignedData, isDigestProvided: true}, nil
 }
 
-// SignerInfoConfig are optional values to include when adding a signer
+// SignerInfoConfig contains configuration options for the signer information.
+// It allows specifying additional signed and unsigned attributes, as well as
+// an option to skip adding certificates to the payload.
 type SignerInfoConfig struct {
-	ExtraSignedAttributes   []Attribute
-	ExtraUnsignedAttributes []Attribute
-	SkipCertificates        bool // Skip adding certificates to the payload
+	ExtraSignedAttributes   []Attribute // Additional attributes to be included in the signed attributes.
+	ExtraUnsignedAttributes []Attribute // Additional attributes to be included in the unsigned attributes.
+	SkipCertificates        bool        // Skip adding certificates to the payload
 }
 
 type signedData struct {

pkcs7/verify.go

@@ -170,7 +170,6 @@ func parseSignedData(data []byte) (*PKCS7, error) {
 	if err != nil {
 		return nil, err
 	}
-	// fmt.Printf("--> Signed Data Version %d\n", sd.Version)
 
 	var compound asn1.RawValue
 	var content unsignedData