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java - 分两步创建 SHA256withRSA

问题描述

出于教育目的，我希望能够首先为字符串创建一个哈希，然后从该哈希创建 RSA 数字签名，以便结果与一次性使用 SHA256withRSA 时相同。通过这种方式，我想确认我完全理解当我们调用 SHA256withRSA 时实际上为我们自动完成的所有步骤。

我还有一个额外的问题。数字签名是在散列还是 Base64 编码散列上完成的？

下面是我目前正在使用的代码，这里是代码的输出，它显示这两种方法产生不同的签名，这意味着我缺少 soma 手动步骤。

AUTOMATICALLY SIGN & VERIFY
SIGNATURE = Hj6a86sR2cJoQFolbxj0blk2I9CAdTdx6WOles5t/pyUyJwa9rp2/SRx2wyXWgc6GsvoZYGLUedeJ2Lklm5hYgT/TtNBATk5eChgfkJMz3NBIRPrsl7ZPG7Wvo4VmHsPpoZZ8PdRk8qY9RLou86OyIqRcX62isuV+e/0deHJ+yTZz4vqA3y+PE4yRFp96A8sKw5VlDnByn7bsxM/QOS+sQWTsETzU9s4YSRfKNq1Urn8/VDoel7n0ORjR918P+0kwE+G77bAOI70yQZorvmbgrMLSBJeVzkKzM/YECLWyrJsqdjfp86FkA9MPGB1V6rO8q8m5GhNoJOmNhC7Ek95Bw==

MANUALLY SIGN & VERIFY
HASH      = lDlahWCWx2b5TYUji52uPeReSW7vbro2wXuRsPKmOdA=
SIGNATURE = gsxw7UQpqni5HyPAw8wI2pvepbrDzizkOvO0hab1+7vi4EaYJi3n4lvnkBTOU5LXQKLZGzJcug0mL2pL/PVh8lrvzZ/F9CxULLxKpayrNkvL9yEWMvcfcku9Go5EGrxSzD7VYvkwOzHvGe4GgUGD1JOjvzXBAfJRT8h/wnZi9IPA9n31/tWI2eFw17Js/gymElycp7pjrpEhUNe/IVTP9HVfRQfAxEDAPW8GY/WFdxbD3Jk05LKvpTxua4jzCX9wJh/s8aiT9OvEXh3/zt06JSEpfgf+CpkOFJupmRhsgqebPfVQEo24ctw1DnipKkL771mm30bFcm/FF1reXuOqqQ==

public class Main {

  //====================================================================================
  // MAIN
  //====================================================================================
  public static void main(String[] args) throws Exception {

    //CREATE DATA
    String            dataString = "Data to be encrypted";
    byte[]            dataBytes  = dataString.getBytes();

    //CREATE KEYS
    KeyPairGenerator  keyPairGenerator = KeyPairGenerator.getInstance("RSA");
                      keyPairGenerator.initialize(2048);
    KeyPair           keyPair    = keyPairGenerator.generateKeyPair();
    PrivateKey        privateKey = keyPair.getPrivate();

    //AUTOMATICALLY SIGN & VERIFY
    System.out.println("\nAUTOMATICALLY SIGN & VERIFY");
    byte[]  automaticSignatureBytes = AutomaticHash.sign  ("SHA256withRSA", privateKey, dataBytes);

    //MANUALLY SIGN & VERIFY
    System.out.println("\nMANUALLY SIGN & VERIFY");
    byte[]  manualHashBytes         = ManualHash.hash  ("SHA-256", dataBytes);
    byte[]  manualSignatureBytes    = ManualHash.sign  ("NONEwithRSA", privateKey, manualHashBytes);

  }

}

public class AutomaticHash {

  //====================================================================================
  // AUTOMATICALLY SIGN
  //====================================================================================
  public static byte[] sign(String algorithms, PrivateKey privateKey, byte[] dataBytes) throws Exception {

    //CREATE SIGNATURE (use Hash first)
    Signature         signature = Signature.getInstance(algorithms);
                      signature.initSign(privateKey);
                      signature.update(dataBytes);
    byte[]            signatureBytes = signature.sign();

    //ENCODE SIGNATURE
    byte[]            signatureEncodedBytes  = Base64.getEncoder().encode(signatureBytes);
    String            signatureEncodedString = new String(signatureEncodedBytes);

    //DISPLAY ENCODED SIGNATURE
    System.out.println("SIGNATURE = " + signatureEncodedString);

    //RETURN SIGNATURE
    return signatureBytes;

  }

}

public class ManualHash {

  //====================================================================================
  // MANUALLY HASH
  //====================================================================================
  public static byte[] hash(String algorithm, byte[] dataBytes) throws Exception {

    //CREATE HASH
    MessageDigest digest    = MessageDigest.getInstance(algorithm);
    byte[]        hashBytes = digest.digest(dataBytes);

    //ENCODE HASH
    byte[]        hashEncoded = Base64.getEncoder().encode(hashBytes);
    String        hashEncodedString = new String(hashEncoded);

    //DISPLAY ENCODED HASH
    System.out.println("HASH      = " + hashEncodedString);

    //RETURN HASH
    return hashBytes;

  }

  //====================================================================================
  // MANUALLY SIGN
  //====================================================================================
  public static byte[] sign(String algorithm, PrivateKey privateKey, byte[] hashBytes) throws Exception {

    //SIGN HASH
    Signature         signature = Signature.getInstance(algorithm);
                      signature.initSign(privateKey);
                      signature.update(hashBytes);
    byte[]            signatureBytes = signature.sign();

    //ENCODE SIGNATURE
    byte[]            signatureEncodedBytes = Base64.getEncoder().encode(signatureBytes);
    String            signatureEncodedString = new String(signatureEncodedBytes);

    //DISPLAY ENCODED HASH & SIGNATURE
    System.out.println("SIGNATURE = " + signatureEncodedString);

    //RETURN SIGNATURE
    return signatureBytes;

  }

}

标签： javahashsignaturedigital

解决方案

SHA256withRSA并NoneWithRSA使用 PKCS#1 v1.5 填充，更准确地说是 RSASSA-PKCS1-v1_5。这是一个确定性填充，即使用相同数据重复签名将产生相同的签名。详细信息可以在RFC8017, 8.2 中找到。

当字节序列(0x)30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20附加到散列时，此填充应用针对 SHA256生成的DigestInfo的 DER 编码。

因此，必须修改您的手动代码，例如如下：

public static byte[] sign(String algorithm, PrivateKey privateKey, byte[] hashBytes) throws Exception {

    byte[] id = new byte[] { 0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, (byte) 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20 };
    byte[] derDigestInfo = new byte[id.length + hashBytes.length];
    System.arraycopy(id, 0, derDigestInfo, 0, id.length);
    System.arraycopy(hashBytes, 0, derDigestInfo, id.length, hashBytes.length);

    // SIGN HASH
    Signature signature = Signature.getInstance(algorithm);
    signature.initSign(privateKey);
    signature.update(derDigestInfo);
    byte[] signatureBytes = signature.sign();

    ...

通过此更改，两种sign()方法都返回相同的结果。

顺便说一句，直接生成一个 Base64 编码的字符串。java.util.Base64.Encoder.encodeToString()

此外，在编码/解码时，应始终指定字符集，例如dataString.getBytes(StandardCharsets.UTF_8)或new String(..., StandardCharsets.UTF_8)。否则将使用平台的默认字符集，这可能与预期的不同。

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