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Crypto: Define ElG length constants

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zzz
2018-11-25 15:23:17 +00:00
parent 9badfd07bf
commit b93be8bb4a
2 changed files with 28 additions and 22 deletions
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27
core/java/src/net/i2p/crypto/ElGamalEngine.java
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@ -58,6 +58,9 @@ public final class ElGamalEngine {
private final YKGenerator _ykgen;
private static final BigInteger ELGPM1 = CryptoConstants.elgp.subtract(BigInteger.ONE);
private static final int ELG_CLEARTEXT_LENGTH = 222;
private static final int ELG_ENCRYPTED_LENGTH = 514;
private static final int ELG_HALF_LENGTH = ELG_ENCRYPTED_LENGTH / 2;
/**
@ -113,8 +116,8 @@ public final class ElGamalEngine {
* the cleartext to 222 bytes with random data.
*/
public byte[] encrypt(byte data[], PublicKey publicKey) {
if ((data == null) || (data.length >= 223))
throw new IllegalArgumentException("Data to encrypt must be < 223 bytes at the moment");
if ((data == null) || (data.length > ELG_CLEARTEXT_LENGTH))
throw new IllegalArgumentException("Data to encrypt must be <= 222 bytes");
if (publicKey == null) throw new IllegalArgumentException("Null public key specified");
long start = _context.clock().now();
@ -149,11 +152,11 @@ public final class ElGamalEngine {
byte[] ybytes = y.toByteArray();
byte[] dbytes = d.toByteArray();
byte[] out = new byte[514];
System.arraycopy(ybytes, 0, out, (ybytes.length < 257 ? 257 - ybytes.length : 0),
(ybytes.length > 257 ? 257 : ybytes.length));
System.arraycopy(dbytes, 0, out, (dbytes.length < 257 ? 514 - dbytes.length : 257),
(dbytes.length > 257 ? 257 : dbytes.length));
byte[] out = new byte[ELG_ENCRYPTED_LENGTH];
System.arraycopy(ybytes, 0, out, (ybytes.length < ELG_HALF_LENGTH ? ELG_HALF_LENGTH - ybytes.length : 0),
(ybytes.length > ELG_HALF_LENGTH ? ELG_HALF_LENGTH : ybytes.length));
System.arraycopy(dbytes, 0, out, (dbytes.length < ELG_HALF_LENGTH ? ELG_ENCRYPTED_LENGTH - dbytes.length : ELG_HALF_LENGTH),
(dbytes.length > ELG_HALF_LENGTH ? ELG_HALF_LENGTH : dbytes.length));
/*
StringBuilder buf = new StringBuilder(1024);
buf.append("Timing\n");
@ -190,18 +193,18 @@ public final class ElGamalEngine {
* @return unencrypted data or null on failure
*/
public byte[] decrypt(byte encrypted[], PrivateKey privateKey) {
if ((encrypted == null) || (encrypted.length != 514))
throw new IllegalArgumentException("Data to decrypt must be exactly 514 bytes");
if ((encrypted == null) || (encrypted.length != ELG_ENCRYPTED_LENGTH))
throw new IllegalArgumentException("Data to decrypt must be exactly ELG_ENCRYPTED_LENGTH bytes");
long start = _context.clock().now();
BigInteger a = new NativeBigInteger(1, privateKey.getData());
BigInteger y1p = ELGPM1.subtract(a);
// we use this buf first for Y, then for D, then for the hash
byte[] buf = SimpleByteCache.acquire(257);
System.arraycopy(encrypted, 0, buf, 0, 257);
byte[] buf = SimpleByteCache.acquire(ELG_HALF_LENGTH);
System.arraycopy(encrypted, 0, buf, 0, ELG_HALF_LENGTH);
NativeBigInteger y = new NativeBigInteger(1, buf);
BigInteger ya = y.modPowCT(y1p, CryptoConstants.elgp);
System.arraycopy(encrypted, 257, buf, 0, 257);
System.arraycopy(encrypted, ELG_HALF_LENGTH, buf, 0, ELG_HALF_LENGTH);
BigInteger d = new NativeBigInteger(1, buf);
BigInteger m = ya.multiply(d);
m = m.mod(CryptoConstants.elgp);