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October 8, 2021 17:16
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Java: convert between ASN.1 and P1363 Encoding of Signature
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import org.bouncycastle.asn1.ASN1EncodableVector; | |
import org.bouncycastle.asn1.ASN1Integer; | |
import org.bouncycastle.asn1.ASN1Sequence; | |
import org.bouncycastle.asn1.DERSequence; | |
import java.math.BigInteger; | |
private static byte[] toP1363(byte[] asn1EncodedSignature) throws Exception { | |
ASN1Sequence seq = ASN1Sequence.getInstance(asn1EncodedSignature); | |
BigInteger r = ((ASN1Integer) seq.getObjectAt(0)).getValue(); | |
BigInteger s = ((ASN1Integer) seq.getObjectAt(1)).getValue(); | |
int n = (r.bitLength() + 7) / 8; | |
// round up to nearest even integer | |
n = (int) Math.round((n+1)/2) * 2; | |
byte[] out = new byte[2 * n]; | |
toFixed(r, out, 0, n); | |
toFixed(s, out, n, n); | |
return out; | |
} | |
private static byte[] toASN1(byte[] p1363EncodedSignature) throws IOException { | |
int n = p1363EncodedSignature.length / 2; | |
BigInteger r = new BigInteger(+1, Arrays.copyOfRange(p1363EncodedSignature, 0, n)); | |
BigInteger s = new BigInteger(+1, Arrays.copyOfRange(p1363EncodedSignature, n, n * 2)); | |
ASN1EncodableVector v = new ASN1EncodableVector(); | |
v.add(new ASN1Integer(r)); | |
v.add(new ASN1Integer(s)); | |
return new DERSequence(v).getEncoded(); | |
} |
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Hi there, I found a better solution for
toP1363
that relies 100% on the BouncyCastle library and works on Android (you don't need to add BouncyCastle as a global provider, you can add the dependency and use the code below as is):