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PseudoRandomFunction.java
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PseudoRandomFunction.java
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/*
* TLS-Attacker - A Modular Penetration Testing Framework for TLS
*
* Copyright 2014-2023 Ruhr University Bochum, Paderborn University, Technology Innovation Institute, and Hackmanit GmbH
*
* Licensed under Apache License, Version 2.0
* http://www.apache.org/licenses/LICENSE-2.0.txt
*/
package de.rub.nds.tlsattacker.core.crypto;
import de.rub.nds.modifiablevariable.util.ArrayConverter;
import de.rub.nds.tlsattacker.core.constants.MacAlgorithm;
import de.rub.nds.tlsattacker.core.constants.PRFAlgorithm;
import de.rub.nds.tlsattacker.core.exceptions.CryptoException;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
/** Pseudo random function computation for SSL3, TLS 1.0 - 1.2 */
public class PseudoRandomFunction {
private static final Logger LOGGER = LogManager.getLogger();
/** master secret label */
public static final String MASTER_SECRET_LABEL = "master secret";
/** client finished label */
public static final String CLIENT_FINISHED_LABEL = "client finished";
/** server finished label */
public static final String SERVER_FINISHED_LABEL = "server finished";
/** key expansion label */
public static final String KEY_EXPANSION_LABEL = "key expansion";
/** extended master secret */
public static final String EXTENDED_MASTER_SECRET_LABEL = "extended master secret";
public static final String CLIENT_WRITE_KEY_LABEL = "client write key";
public static final String SERVER_WRITE_KEY_LABEL = "server write key";
public static final String IV_BLOCK_LABEL = "IV block";
/**
* sByte is a constant additional salt byte that is used in the computeSSL3 method for computing
* a pseudo random bit stream as described in the RFC 6101
*/
private static final byte sByte = 0x41;
/**
* Computes the PRF output for SSL3 of the provided size
*
* @param master_secret the master secret
* @param client_random the client random
* @param server_random the server random
* @param size the size of the key block
* @return the key block as pseudo random bit stream
* @throws NoSuchAlgorithmException
*/
public static byte[] computeSSL3(
byte[] master_secret, byte[] client_random, byte[] server_random, int size)
throws NoSuchAlgorithmException, IOException {
MessageDigest md5 = MessageDigest.getInstance("MD5");
MessageDigest sha1 = MessageDigest.getInstance("SHA-1");
ByteArrayOutputStream pseudoRandomBitStream = new ByteArrayOutputStream();
/*
* RFC 6101: 6.1. Converting the Master Secret into Keys and MAC Secrets To generate the key material, compute
* pseudoRandomBitStream = MD5(master_secret + SHA(`A' + master_secret + ServerHello.random +
* ClientHello.random)) + MD5(master_secret + SHA(`BB' + master_secret + ServerHello.random +
* ClientHello.random)) + MD5(master_secret + SHA(`CCC' + master_secret + ServerHello.random +
* ClientHello.random)) + [...]; until enough output has been generated.
*/
for (int i = 0; pseudoRandomBitStream.size() <= size; i++) {
ByteArrayOutputStream outputMd5 = new ByteArrayOutputStream();
ByteArrayOutputStream outputSha = new ByteArrayOutputStream();
ByteArrayOutputStream salt = new ByteArrayOutputStream();
for (int j = 0; j <= i; j++) {
salt.write(sByte + i);
}
outputSha.write(
sha1.digest(
ArrayConverter.concatenate(
salt.toByteArray(),
master_secret,
server_random,
client_random)));
outputMd5.write(
md5.digest(ArrayConverter.concatenate(master_secret, outputSha.toByteArray())));
pseudoRandomBitStream.write(outputMd5.toByteArray());
}
return Arrays.copyOf(pseudoRandomBitStream.toByteArray(), size);
}
/**
* Computes the PRF output for TLS1.0 - TLS1.2 of the provided size using the given mac
* algorithm
*
* @param prfAlgorithm PRFAlgorithm
* @param secret The Secret
* @param label The Label
* @param seed The Seed
* @param size The size
* @return the Prf output
* @throws de.rub.nds.tlsattacker.core.exceptions.CryptoException
*/
public static byte[] compute(
PRFAlgorithm prfAlgorithm, byte[] secret, String label, byte[] seed, int size)
throws CryptoException {
if (prfAlgorithm == null) {
LOGGER.warn(
"Trying to compute PRF without specified PRF algorithm. Using TLS 1.0/TLS 1.1 as default.");
prfAlgorithm = PRFAlgorithm.TLS_PRF_LEGACY;
}
if (secret == null) {
LOGGER.warn(
"Secret is null! Continuing to compute PRF with a secret set to zero bytes...");
secret = new byte[0];
}
if (prfAlgorithm == PRFAlgorithm.TLS_PRF_LEGACY) {
return computeTls10(secret, label, seed, size);
} else {
switch (prfAlgorithm) {
case TLS_PRF_SHA256:
return computeTls12(secret, label, seed, size, MacAlgorithm.HMAC_SHA256);
case TLS_PRF_SHA384:
return computeTls12(secret, label, seed, size, MacAlgorithm.HMAC_SHA384);
case TLS_PRF_GOSTR3411:
return computeTls12(secret, label, seed, size, MacAlgorithm.HMAC_GOSTR3411);
case TLS_PRF_GOSTR3411_2012_256:
return computeTls12(
secret, label, seed, size, MacAlgorithm.HMAC_GOSTR3411_2012_256);
default:
throw new UnsupportedOperationException(
"PRF computation for different"
+ " protocol versions is not supported yet");
}
}
}
private static byte[] computeTls10(byte[] secret, String label, byte[] seed, int size)
throws CryptoException {
try {
byte[] labelSeed =
ArrayConverter.concatenate(label.getBytes(Charset.forName("ASCII")), seed);
byte[] pseudoRandomBitStream = new byte[size];
HMAC hmacMd5 = new HMAC(MacAlgorithm.HMAC_MD5);
HMAC hmacSha1 = new HMAC(MacAlgorithm.HMAC_SHA1);
/*
* Divides the secret into two halves, s1 and s2
*/
int secretHalf = (secret.length + 1) / 2;
byte[] s1 = new byte[secretHalf];
byte[] s2 = new byte[secretHalf];
System.arraycopy(secret, 0, s1, 0, secretHalf);
System.arraycopy(secret, secret.length - secretHalf, s2, 0, secretHalf);
hmacMd5.init(s1);
hmacSha1.init(s2);
/*
* Expands the first half of the secret with the p_hash function, which uses md5
*/
byte[] extendedSecretMd5 = p_hash(hmacMd5, labelSeed, size);
/*
* Expands the second half of the secret with the p_hash function, which uses sha1
*/
byte[] extendedSecretSha1 = p_hash(hmacSha1, labelSeed, size);
/*
* Produces the pseudo random bit stream by xoring the extended secrets
*/
for (int i = 0; i < size; i++) {
pseudoRandomBitStream[i] = (byte) (extendedSecretMd5[i] ^ extendedSecretSha1[i]);
}
return pseudoRandomBitStream;
} catch (NoSuchAlgorithmException | IOException ex) {
throw new CryptoException(ex);
}
}
/**
* PRF computation for TLS 1.2 s
*
* @param macAlgorithm PRFAlgorithm
* @param secret The Secret
* @param label The Label
* @param seed The Seed
* @param size The size of the pseudo random bit stream
* @return the key block material
*/
private static byte[] computeTls12(
byte[] secret, String label, byte[] seed, int size, MacAlgorithm macAlgorithm)
throws CryptoException {
try {
byte[] labelSeed =
ArrayConverter.concatenate(label.getBytes(Charset.forName("ASCII")), seed);
HMAC hmac = new HMAC(macAlgorithm);
hmac.init(secret);
/*
* Expands the secret to produce the pseudo random bit stream
*/
byte[] pseudoRandomBitStream = p_hash(hmac, labelSeed, size);
return pseudoRandomBitStream;
} catch (NoSuchAlgorithmException | IOException ex) {
throw new CryptoException(ex);
}
}
/*
* RFC 5246 5. HMAC and the Pseudorandom Function p_hash is a data expansion function. By taking a secret and a seed
* as input, a data expansion function produces an output of arbitrary length. In here, p_hash only computes one
* round of pseudo random bits (one use of the hmac) To expand the secret, one can implement a PRF with p_hash as
* follows: P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) + HMAC_hash(secret, A(2) + seed) +
* HMAC_hash(secret, A(3) + seed) + ... where + indicates concatenation. A() is defined as: A(0) = seed A(i) =
* HMAC_hash(secret, A(i-1)) TLS's PRF is created by applying P_hash to the secret as: PRF(secret, label, seed) =
* P_<hash>(secret, label + seed)
*
* The PseudoRandomFunction class takes use of the p_hash function.
*/
/**
* p_hash is a data expansion function as described in RFC 5246 5. HMAC and the Pseudorandom
* Function
*
* @param hmac
* @param data
* @param size
* @return
* @throws NoSuchAlgorithmException
*/
private static byte[] p_hash(HMAC hmac, byte[] data, int size)
throws NoSuchAlgorithmException, IOException {
ByteArrayOutputStream extendedSecret = new ByteArrayOutputStream();
/*
* hmacIteration will be used as an input for the next hmac, which will generate the actual bytes for the
* extendedSecret
*/
byte[] hmacIteration = data;
/*
* Expands the secret
*/
while (extendedSecret.size() < size) {
hmacIteration = hmac.doFinal(hmacIteration);
extendedSecret.write(hmac.doFinal(ArrayConverter.concatenate(hmacIteration, data)));
}
return Arrays.copyOf(extendedSecret.toByteArray(), size);
}
private PseudoRandomFunction() {}
}