diff options
Diffstat (limited to 'libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/signers/DSASigner.java')
-rw-r--r-- | libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/signers/DSASigner.java | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/signers/DSASigner.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/signers/DSASigner.java new file mode 100644 index 000000000..4d9b87842 --- /dev/null +++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/signers/DSASigner.java @@ -0,0 +1,160 @@ +package org.spongycastle.crypto.signers; + +import java.math.BigInteger; +import java.security.SecureRandom; + +import org.spongycastle.crypto.CipherParameters; +import org.spongycastle.crypto.DSA; +import org.spongycastle.crypto.params.DSAKeyParameters; +import org.spongycastle.crypto.params.DSAParameters; +import org.spongycastle.crypto.params.DSAPrivateKeyParameters; +import org.spongycastle.crypto.params.DSAPublicKeyParameters; +import org.spongycastle.crypto.params.ParametersWithRandom; + +/** + * The Digital Signature Algorithm - as described in "Handbook of Applied + * Cryptography", pages 452 - 453. + */ +public class DSASigner + implements DSA +{ + private final DSAKCalculator kCalculator; + + private DSAKeyParameters key; + private SecureRandom random; + + /** + * Default configuration, random K values. + */ + public DSASigner() + { + this.kCalculator = new RandomDSAKCalculator(); + } + + /** + * Configuration with an alternate, possibly deterministic calculator of K. + * + * @param kCalculator a K value calculator. + */ + public DSASigner(DSAKCalculator kCalculator) + { + this.kCalculator = kCalculator; + } + + public void init( + boolean forSigning, + CipherParameters param) + { + if (forSigning) + { + if (param instanceof ParametersWithRandom) + { + ParametersWithRandom rParam = (ParametersWithRandom)param; + + this.random = rParam.getRandom(); + this.key = (DSAPrivateKeyParameters)rParam.getParameters(); + } + else + { + this.random = new SecureRandom(); + this.key = (DSAPrivateKeyParameters)param; + } + } + else + { + this.key = (DSAPublicKeyParameters)param; + } + } + + /** + * generate a signature for the given message using the key we were + * initialised with. For conventional DSA the message should be a SHA-1 + * hash of the message of interest. + * + * @param message the message that will be verified later. + */ + public BigInteger[] generateSignature( + byte[] message) + { + DSAParameters params = key.getParameters(); + BigInteger m = calculateE(params.getQ(), message); + + if (kCalculator.isDeterministic()) + { + kCalculator.init(params.getQ(), ((DSAPrivateKeyParameters)key).getX(), message); + } + else + { + kCalculator.init(params.getQ(), random); + } + + BigInteger k = kCalculator.nextK(); + + BigInteger r = params.getG().modPow(k, params.getP()).mod(params.getQ()); + + k = k.modInverse(params.getQ()).multiply( + m.add(((DSAPrivateKeyParameters)key).getX().multiply(r))); + + BigInteger s = k.mod(params.getQ()); + + BigInteger[] res = new BigInteger[2]; + + res[0] = r; + res[1] = s; + + return res; + } + + /** + * return true if the value r and s represent a DSA signature for + * the passed in message for standard DSA the message should be a + * SHA-1 hash of the real message to be verified. + */ + public boolean verifySignature( + byte[] message, + BigInteger r, + BigInteger s) + { + DSAParameters params = key.getParameters(); + BigInteger m = calculateE(params.getQ(), message); + BigInteger zero = BigInteger.valueOf(0); + + if (zero.compareTo(r) >= 0 || params.getQ().compareTo(r) <= 0) + { + return false; + } + + if (zero.compareTo(s) >= 0 || params.getQ().compareTo(s) <= 0) + { + return false; + } + + BigInteger w = s.modInverse(params.getQ()); + + BigInteger u1 = m.multiply(w).mod(params.getQ()); + BigInteger u2 = r.multiply(w).mod(params.getQ()); + + u1 = params.getG().modPow(u1, params.getP()); + u2 = ((DSAPublicKeyParameters)key).getY().modPow(u2, params.getP()); + + BigInteger v = u1.multiply(u2).mod(params.getP()).mod(params.getQ()); + + return v.equals(r); + } + + private BigInteger calculateE(BigInteger n, byte[] message) + { + if (n.bitLength() >= message.length * 8) + { + return new BigInteger(1, message); + } + else + { + byte[] trunc = new byte[n.bitLength() / 8]; + + System.arraycopy(message, 0, trunc, 0, trunc.length); + + return new BigInteger(1, trunc); + } + } +} |