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POCalculating ECDSA signature in Java as per an RFC test vector
 

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  1. POCalculating ECDSA signature in Java as per an RFC test vector
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    <p>I am writing a test harness in java for a program relating to the ikev2 protocol. As part of this i need to be able to calculate an ECDSA signature (specifically using the NIST P-256 curve).</p> <p><a href="http://tools.ietf.org/html/rfc4754" rel="nofollow">RFC 4754</a> Describes the the use of ECDSA in IKEv2 and helpfully provides a set of test vectors (Including for the p256 curve that i need).</p> <p>I am trying to run the ECDSA-256 Test Vector values (<a href="http://tools.ietf.org/html/rfc4754#section-8.1" rel="nofollow">Section 8.1</a> in the RFC) through java's ECDSA signature implementation using the following code:</p> <pre><code>//"abc" for the input byte[] input = { 0x61, 0x62, 0x63 }; //Ugly way of getting the ECParameterSpec for the P-256 curve by name as opposed to specifying all the parameters manually. KeyPairGenerator kpg = KeyPairGenerator.getInstance("EC"); ECGenParameterSpec kpgparams = new ECGenParameterSpec("secp256r1"); kpg.initialize(kpgparams); ECParameterSpec params = ((ECPublicKey) kpg.generateKeyPair().getPublic()).getParams(); //Create the static private key W from the Test Vector ECPrivateKeySpec static_privates = new ECPrivateKeySpec(new BigInteger("DC51D3866A15BACDE33D96F992FCA99DA7E6EF0934E7097559C27F1614C88A7F", 16), params); KeyFactory kf = KeyFactory.getInstance("EC"); ECPrivateKey spriv = (ECPrivateKey) kf.generatePrivate(static_privates); //Perfrom ECDSA signature of the data with SHA-256 as the hash algorithm Signature dsa = Signature.getInstance("SHA256withECDSA"); dsa.initSign(spriv); dsa.update(input); byte[] output = dsa.sign(); System.out.println("Result: " + new BigInteger(1, output).toString(16)); </code></pre> <p>The result should be:</p> <blockquote> <p>CB28E099 9B9C7715 FD0A80D8 E47A7707 9716CBBF 917DD72E 97566EA1 C066957C 86FA3BB4 E26CAD5B F90B7F81 899256CE 7594BB1E A0C89212 748BFF3B 3D5B0315</p> </blockquote> <p>Instead I get:</p> <blockquote> <p>30460221 00dd9131 edeb5efd c5e718df c8a7ab2d 5532b85b 7d4c012a e5a4e90c 3b824ab5 d7022100 9a8a2b12 9e10a2ff 7066ff79 89aa73d5 ba37c868 5ec36517 216e2e43 ffa876d7</p> </blockquote> <p>I know that the length difference is due to Java ASN.1 Encoding the signature. However, the rest of it is completely wrong and I'm stumped as to why.</p> <p>Any help or advice would be greatly appreciated!</p> <p>P.S I am not a ECDSA or Java crypto expert so it is probably a stupid mistake I am making</p>
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