使用SM2密钥签名时，仅支持对消息摘要签名。

根据GBT32918国家标准，计算SM2签名值时，消息摘要不是对原始消息直接计算SM3摘要，而是对Z(A)和M的拼接值计算的摘要。其中M是待签名的原始消息，Z(A)是GBT32918中定义的用户A的杂凑值。

以JAVA为例，参考如下示例代码：

public class Sm2SignDataPreprocessing { 
 
    private static final String ECC_A = "FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC"; 
    private static final String ECC_B = "28E9FA9E9D9F5E344D5A9E4BCF6509A7F39789F515AB8F92DDBCBD414D940E93"; 
    private static final String ECC_GX = "32C4AE2C1F1981195F9904466A39C9948FE30BBFF2660BE1715A4589334C74C7"; 
    private static final String ECC_GY = "BC3736A2F4F6779C59BDCEE36B692153D0A9877CC62A474002DF32E52139F0A0"; 
 
    // 签名者ID，本示例使用国密标准定义的缺省值"1234567812345678" 
    private static final String SM2_ID = "31323334353637383132333435363738"; 
 
    public static void main(String[] args) throws Exception { 
 
        // SM2公钥，BASE64编码格式，仅做示例，实际使用请替换 
        String sm2PubKey = "MFkwEwYHKoZIzj0CAQYIKoEcz1UBgi0DQgAEsuOq/EjQeYUD9h7lIyqi3pQ6SWL7hTXjUJWmSIZAcnj" + 
                "h9c0QcdbwzaCfI8iyyPCetX0QZl5NHrBoYLYxJpvbFg=="; 
 
        byte[] pubKeyBytes = Base64.decodeBase64(sm2PubKey.getBytes(StandardCharsets.UTF_8)); 
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(pubKeyBytes); 
        KeyFactory keyFactory = KeyFactory.getInstance("EC", new BouncyCastleProvider()); 
        ECPublicKey ecPublicKey = (ECPublicKey) keyFactory.generatePublic(keySpec); 
 
        // 待签名的原始消息，仅做示例，实际使用请替换 
        byte[] dataToDigest = new byte[]{1, 2, 3, 4}; 
 
        // Z(A)是GBT32918中定义的用户A的杂凑值 
        byte[] zsm = getSm2Z(ecPublicKey.getQ().getAffineXCoord().getEncoded(), 
                ecPublicKey.getQ().getAffineYCoord().getEncoded()); 
 
        // Z(A)和M的拼接值计算的摘要，并打印 
        byte[] dataToSign = getSm3SignData(zsm, dataToDigest); 
        System.out.println(Base64.encodeBase64String(dataToSign)); 
 
        // 其他语言实现或执行此示例应有如下输出：He+qiM2MmtNxlV/EB4vqkcP60XgG08z/8nWQdp/IS5c= 
    } 
 
    // 计算Z(A) 
    private static byte[] getSm2Z(byte[] x, byte[] y) throws DecoderException { 
        SM3Digest sm3 = new SM3Digest(); 
        byte[] userId = Hex.decodeHex(SM2_ID.toCharArray()); 
        byte[] byteEccA = Hex.decodeHex(ECC_A); 
        byte[] byteEccB = Hex.decodeHex(ECC_B); 
        byte[] byteEccGx = Hex.decodeHex(ECC_GX); 
        byte[] byteEccGy = Hex.decodeHex(ECC_GY); 
        int len = userId.length * 8; 
        sm3.update((byte) (len >> 8 & 255)); 
        sm3.update((byte) (len & 255)); 
        sm3.update(userId, 0, userId.length); 
        sm3.update(byteEccA, 0, byteEccA.length); 
        sm3.update(byteEccB, 0, byteEccB.length); 
        sm3.update(byteEccGx, 0, byteEccGx.length); 
        sm3.update(byteEccGy, 0, byteEccGy.length); 
        sm3.update(x, 0, x.length); 
        sm3.update(y, 0, y.length); 
        byte[] md = new byte[sm3.getDigestSize()]; 
        sm3.doFinal(md, 0); 
        return md; 
    } 
 
    // 计算Z(A)和M的拼接值的摘要 
    private static byte[] getSm3SignData(byte[] z, byte[] sourceData) { 
        SM3Digest sm3 = new SM3Digest(); 
        sm3.update(z, 0, z.length); 
        sm3.update(sourceData, 0, sourceData.length); 
        byte[] md = new byte[sm3.getDigestSize()]; 
        sm3.doFinal(md, 0); 
        return md; 
    } 
 
}