[英]How do I ECDSA verify a block of data in Java when I only have the raw signature (R, S) and raw public key point (Qx, Qy)
我有一個字節數組消息以及簽名的四個 32 字節原始組件: Qx 、 Qy 、 R和S 。 如何將這些格式化/編碼為Signature::verify
function 期望的ECPublicKey
和簽名byte[]
? 簽名是使用 SHA-256 ECDSA 創建的。
該解決方案需要結合其他兩個答案(並在 Java 中實現):
創建公鑰涉及生成一個虛擬密鑰對並使用其ECParameterSpec
,然后替換您的原始公鑰點 [Qx, Qy]。 還必須從原始字節創建BigInteger
。 這可以在下面的createPublicKey
function 中看到。
簽名(由 R 和 S 組成)必須以DER 格式編碼 - 我找不到現有的 Java 實用程序createDERSigniture
手動完成,如下所示。
/**
* Check to see if `message` matches signature [R, S] and public key point [qx, qy]
*
* @param message device ID
* @param r first part of the ECDSA signature
* @param s second part of the ECDSA signature
* @param qx x part of the public key point
* @param qy y part of the public key point
* @return true iff the signature signed the message
* @note ECDSA SHA-256 is used - r, s, qx and qy must be 32 bytes long
*/
private static boolean ecdsaVerify(@NotNull final byte[] message, @NotNull final byte[] r, @NotNull final byte[] s,
@NotNull final byte[] qx, @NotNull final byte[] qy)
{
try
{
// convert from raw bytes to something `Signature` can understand
ECPublicKey publicKey = createPublicKey(qx, qy);
byte[] derSignature = createDERSigniture(r, s);
// do the actual verification
Signature sig = Signature.getInstance("SHA256withECDSA");
sig.initVerify(publicKey);
sig.update(message);
return sig.verify(derSignature);
}
catch (NoSuchAlgorithmException | InvalidKeySpecException | InvalidKeyException | SignatureException | InvalidAlgorithmParameterException e)
{
return false;
}
}
/**
* Format the raw elliptic curve point [qx, qy] with the NIST P-256
*
* @param qx the x coordinate - should be 32 bytes
* @param qy the y coordinate - should be 32 bytes
* @return the public key from the raw coordinates
* @see https://stackoverflow.com/a/22652372/1229250
*/
private static ECPublicKey createPublicKey(byte[] qx, byte[] qy)
throws NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeySpecException
{
// generate bogus keypair so we can get its spec
KeyPairGenerator kpg = KeyPairGenerator.getInstance("EC");
kpg.initialize(new ECGenParameterSpec("secp256r1"));// NIST P-256
ECPublicKey apub = (ECPublicKey)kpg.generateKeyPair().getPublic();
ECParameterSpec aspec = apub.getParams();
ECPoint point = new ECPoint(new BigInteger(1, qx), new BigInteger(1, qy));
ECPublicKeySpec pks = new ECPublicKeySpec(point, aspec);
return (ECPublicKey)KeyFactory.getInstance("EC").generatePublic(pks);
}
/**
* Encode a raw signature in the DER format
*
* @param r first part of the raw signature - should be 32 bytes
* @param s second part of the raw signature - should be 32 bytes
* @return a DER formatted signature
* @see https://crypto.stackexchange.com/a/57734/89173
*/
private static byte[] createDERSigniture(byte[] r, byte[] s)
{
// build backwards
byte[] der = {};
der = prependPoint(der, s);
der = prependPoint(der, r);
return prependHeader(der);
}
/**
* Take in a raw coordinate value, `p` and then wrap and prepend it to `derSig`
*
* Wrapping includes adding the header by (0x02), the length as well as a leading zero if needed.
*
* @param derSig the end of the DER formatted signature, so far (may be empty)
* @param p a part of the coordinate to prepend
* @return the signature so far with an addition component
*/
private static byte[] prependPoint(byte[] derSig, byte[] p)
{
// append a zero byte if the leading *bit* is one (so as a whole, it is a positive number)
final boolean prependZero = (p[0] & 0x80) == 0x80;
final int pointLength = p.length + (prependZero ? 1 : 0);
final int prependSize = 2 + pointLength;
final int totalNewSize = prependSize + derSig.length;
byte[] result = new byte[totalNewSize];
result[0] = 2;
result[1] = (byte) pointLength;
if (prependZero)
{
result[2] = 0;
}
System.arraycopy(p, 0, result, prependZero ? 3 : 2, p.length);
System.arraycopy(derSig, 0, result, prependSize, derSig.length);
return result;
}
/**
* Add the DER header - the 0x30 magic number and the length of the point
*
* @param derSig the DER signature so far - must have the two points
* @return the signature with the proper header
*/
private static byte[] prependHeader(byte[] derSig)
{
byte[] result = new byte[derSig.length + 2];
result[0] = 0x30;
result[1] = (byte) derSig.length;
System.arraycopy(derSig, 0, result, 2, derSig.length);
return result;
}
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