generate a SHA256withDSA signature using Go and then verify it using Java

Question

1. Go sha256 orign data then DSA sign it
2. print sign result by hex
3. use Java SHA256withDSA to verify first step result return false
4. i konw sha256 then DSA is difference SHA256withDSA
5. how can i do in Go to generate a sign, that can be verified using sha256withdsa in Java ?
6. do Go has any another third party library support ?

Go

package main

import (
    "crypto/dsa"
    "crypto/rand"
    "crypto/sha256"
    "encoding/asn1"
    "encoding/hex"
    "fmt"
    "golang.org/x/crypto/ssh"
    "math/big"
)

func main() {
    pemData := []byte("-----BEGIN DSA PRIVATE KEY-----\n" +
        "MIIBvAIBAAKBgQD9f1OBHXUSKVLfSpwu7OTn9hG3UjzvRADDHj+AtlEmaUVdQCJR\n" +
        "+1k9jVj6v8X1ujD2y5tVbNeBO4AdNG/yZmC3a5lQpaSfn+gEexAiwk+7qdf+t8Yb\n" +
        "+DtX58aophUPBPuD9tPFHsMCNVQTWhaRMvZ1864rYdcq7/IiAxmd0UgBxwIVAJdg\n" +
        "UI8VIwvMspK5gqLrhAvwWBz1AoGBAPfhoIXWmz3ey7yrXDa4V7l5lK+7+jrqgvlX\n" +
        "TAs9B4JnUVlXjrrUWU/mcQcQgYC0SRZxI+hMKBYTt88JMozIpuE8FnqLVHyNKOCj\n" +
        "rh4rs6Z1kW6jfwv6ITVi8ftiegEkO8yk8b6oUZCJqIPf4VrlnwaSi2ZegHtVJWQB\n" +
        "TDv+z0kqAoGBAIb9o0KPsjAdzjK571e1Mx7ZhEyJGrcxHiN2sW8IztEbqrKKiMxp\n" +
        "NlTwm234uBdtzVHE3uDWZpfHPMIRmwBjCYDFRowWWVRdhdFXZlpCyp1gMWqJ11dh\n" +
        "3FI3+O43DevRSyyuLRVCNQ1J3iVgwY5ndRpZU7n6y8DPH4/4EBT7KvnVAhR4Vwun\n" +
        "Fhu/+4AGaVeMEa814I3dqg==\n" +
        "-----END DSA PRIVATE KEY-----")

    p, _ := ssh.ParseRawPrivateKey(pemData)
    pp := p.(*dsa.PrivateKey)

    hashed := []byte{1}
    sha256 := sha256.New()
    sha256.Write(hashed)
    hashed = sha256.Sum(nil)
    r, s, _ := dsa.Sign(rand.Reader, pp, hashed)
    type dsaSignature struct {
        R, S *big.Int
    }
    var ss dsaSignature
    ss.S = s
    ss.R = r
    signatureBytes, _ := asn1.Marshal(ss)
    fmt.Println(hex.EncodeToString(signatureBytes))
}

Java

 @Test
    public void ttt() throws InvalidKeySpecException, NoSuchAlgorithmException, InvalidKeyException, SignatureException {
        String pubKey = "-----BEGIN PUBLIC KEY-----\n" +
                "MIIBuDCCASwGByqGSM44BAEwggEfAoGBAP1/U4EddRIpUt9KnC7s5Of2EbdSPO9E\n" +
                "AMMeP4C2USZpRV1AIlH7WT2NWPq/xfW6MPbLm1Vs14E7gB00b/JmYLdrmVClpJ+f\n" +
                "6AR7ECLCT7up1/63xhv4O1fnxqimFQ8E+4P208UewwI1VBNaFpEy9nXzrith1yrv\n" +
                "8iIDGZ3RSAHHAhUAl2BQjxUjC8yykrmCouuEC/BYHPUCgYEA9+GghdabPd7LvKtc\n" +
                "NrhXuXmUr7v6OuqC+VdMCz0HgmdRWVeOutRZT+ZxBxCBgLRJFnEj6EwoFhO3zwky\n" +
                "jMim4TwWeotUfI0o4KOuHiuzpnWRbqN/C/ohNWLx+2J6ASQ7zKTxvqhRkImog9/h\n" +
                "WuWfBpKLZl6Ae1UlZAFMO/7PSSoDgYUAAoGBAIb9o0KPsjAdzjK571e1Mx7ZhEyJ\n" +
                "GrcxHiN2sW8IztEbqrKKiMxpNlTwm234uBdtzVHE3uDWZpfHPMIRmwBjCYDFRowW\n" +
                "WVRdhdFXZlpCyp1gMWqJ11dh3FI3+O43DevRSyyuLRVCNQ1J3iVgwY5ndRpZU7n6\n" +
                "y8DPH4/4EBT7KvnV\n" +
                "-----END PUBLIC KEY-----";
        String publicKeyPEM = pubKey
                .replace("-----BEGIN PUBLIC KEY-----\n", "")
                .replaceAll(System.lineSeparator(), "")
                .replace("-----END PUBLIC KEY-----", "");
        byte[] publicEncoded = Base64.decodeBase64(publicKeyPEM);
        KeyFactory keyFactory1 = KeyFactory.getInstance("DSA");
        X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(publicEncoded);
        DSAPublicKey pubKeyy = (DSAPublicKey) keyFactory1.generatePublic(publicKeySpec);

        Signature sig1 = Signature.getInstance("SHA256withDSA");
        sig1.initVerify(pubKeyy);
        byte[] orignData = new byte[]{1};
        sig1.update(orignData);
        boolean flag = sig1.verify(HexUtil.decodeHex("first step result"));
        System.out.println(flag);
    }

Answer 1

follow FIPS186-4 sections 4.6 and 4.7 golang should this

hashed := []byte{1}
pemData, _ := ioutil.ReadFile("config/secure/private.key")
p, err := ssh.ParseRawPrivateKey(pemData)
pp, ok := p.(*dsa.PrivateKey)
h := sha256.New()
h.Write(hashed)
hashed := h.Sum(nil)
if pp.Q.BitLen()/8 < len(hashed) {
    hashed = hashed[0 : pp.Q.BitLen()/8]
}
r, s, _ := dsa.Sign(rand.Reader, pp, hashed)
var ss dsaSignature
ss.S = s
ss.R = r
hashed, _ = asn1.Marshal(ss)

Answer 2

i found in java

package sun.security.provider;

private BigInteger generateS(BigInteger var1, BigInteger var2, BigInteger var3, BigInteger var4) throws SignatureException {
        byte[] var5;
        try {
            var5 = this.md.digest();
        } catch (RuntimeException var9) {
            throw new SignatureException(var9.getMessage());
        }

        // this line split the hash256 redsult
        int var6 = var2.bitLength() / 8;
        if (var6 < var5.length) {
            var5 = Arrays.copyOfRange(var5, 0, var6);
        }

        BigInteger var7 = new BigInteger(1, var5);
        BigInteger var8 = var4.modInverse(var2);
        return var1.multiply(var3).add(var7).multiply(var8).mod(var2);
}

you can use in golang

    hashed := []byte{1}
    sha256 := sha2562.New()
    sha256.Write(hashed)
    hashed = sha256.Sum(nil)
    // you must split it 
    hashed = hashed[0:20]

the reason is sha256 result split in java , but glang not split