EDDSA Signature with Luna HSM using Java

Question

I am trying to implement EDDSA signature with Luna HSM(Gemalto)

Signature signature = null;
signature = Signature.getInstance("EDDSA", "LunaProvider");
PrivateKey privateKey = getPrivateByAlias(privateKeyLabel);
signature.initSign(privateKey);
signature.update(payload);
byte[] byteArray = signature.sign();

But after the signing, the byteArray size is coming as 71, but EDDSA signature size is 64 as per specification. I am not sure what i am missing here. I couldn't find any document either online.

Maarten Bodewes · Accepted Answer · 2020-03-14T16:15:40.000

1

This is exactly a size you would expect for an X9.63 compatible signature, which consists of a DER encoding of two signed big endian integers. If you want to have a 64 byte signature then you should convert the 2 integers inside using the following explanation. An implementation in Java of I2OSP and OS2IP can be found here.

So the steps are:

parse ASN.1 signature;
convert to BigInteger values using the new BigInteger(byte[]) constructor;
use I2OSP to create the r and s values as byte array (32 octet output size);
concatenate the r and s to create the 64 byte signature.

edited Mar 14 '20 at 16:15

answered Mar 14 '20 at 13:27

Maarten Bodewes

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Thanks for the reply, it really helps me a lot, i am trying to convert the DER format to ASN.1 now using BouncyCastle. I will post the code once i managed to do it – Mayuran Mar 15 '20 at 03:25
i have tried the following but it seems that the verification is still failing. – Mayuran Mar 16 '20 at 02:36

Mayuran · Answer 2 · 2020-03-16T09:57:35.680

I have tried as follows but the verification is failing(Code updated and it works now)

        Signature signature = Signature.getInstance("SHA512withEDDSA", "LunaProvider");
        signature.setParameter(new LunaEDDSAParameterSpec(false));
        signature.initSign(privateKey);
        signature.update(payload);
        byte[] byteArray = signature.sign();

        ASN1InputStream decoder = new ASN1InputStream(byteArray);
        DERSequence seq = (DERSequence) decoder.readObject();
        DERInteger r = (DERInteger) seq.getObjectAt(0);
        DERInteger s = (DERInteger) seq.getObjectAt(1);
        LOGGER.info("R: {}", r.getValue());
        LOGGER.info("S: {}", s.getValue());
        decoder.close();

        byte[] rByte = i2osp(r.getValue(), 32);
        byte[] sByte = i2osp(s.getValue(), 32);

        byte[] concat = Bytes.concat(rByte, sByte);

        return concat;

Not sure this is the correct way of doing

Verification using stellar java library

        PublicKey publicKey = getPublicByAlias(publicKeyLabel);
        LunaPublicKeyEC lunaPublicKeyEC = (LunaPublicKeyEC) publicKey;
        byte[] pubKeySub = Arrays.copyOfRange(lunaPublicKeyEC.getP(), 2, lunaPublicKeyEC.getP().length);
        org.stellar.sdk.KeyPair keyPair = org.stellar.sdk.KeyPair.fromPublicKey(pubKeySub);
        boolean verified = keyPair.verify(payload, signatureByte);

@MaartenBodewes Thanks a lot, i managed to do it, i am posting the updated code for others reference. The reason was that the LunaEDDSAParameterSpec default was setting the prehash to true, but i set it to false, then i was able to get the same value as expected by stellar(crypto currency) verification. I am not sure about what is the default for EDDSA. — Mayuran, Mar 16 '20 at 09:56
@MaartenBodewes i use stellar java library to verify the signature, updated the code above with verification as well — Mayuran, Mar 16 '20 at 09:59
Code updated and it works now, does that mean the problem is solved? — Maarten Bodewes, Mar 16 '20 at 10:04

EDDSA Signature with Luna HSM using Java

2 Answers2