Fix potential timing attack due to manually comparing hashes with a loop

mark.george / BouncyScrypt

Browse code Fix potential timing attack due to manually comparing hashes with a loop The number of loop iterations can be used as an indication of how close a guessed hash is to the correct one. master
1 parent a29aae4 commit 2bbdd256a20ac6f0d6a051c85e8f352231bda48e Mark George authored on 6 May

Patch

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Ignore Space Show notes View src/main/java/helpers/ScryptHelper.java
package helpers; import java.nio.ByteBuffer; import java.nio.CharBuffer; import java.nio.charset.Charset; import java.nio.charset.StandardCharsets; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.util.Arrays; import java.util.Base64; import java.util.regex.Matcher; import java.util.regex.Pattern; import org.bouncycastle.crypto.generators.SCrypt; /** * Wrapper for Bouncy Castle's scrypt implementation. * * Generates salted scrypt hashes in a format similar to Modular Crypt Format * (MCF). * * @author Mark George <mark.george@otago.ac.nz> / public final class ScryptHelper { // the standard work factors for scrypt private static final int N = 32768; private static final int r = 8; private static final int p = 1; private static final int saltSize = 64; private static final int dkLen = 64; private static final Charset utf8 = StandardCharsets.UTF_8; private ScryptHelper() { } /* * Generates an MCF-like formatted salted scrypt hash for the password. * * @param password The password to hash. * @return The MCF formatted hash. / public static CharBuffer hash(CharSequence password) { byte[] salt = salt(); byte[] hash = hash(password, salt, N, r, p, dkLen); Base64.Encoder b64encoder = Base64.getEncoder(); int costParams = (log2(N)) << 16 \| r << 8 \| p; byte[] dollar = "$".getBytes(utf8); byte[] params = String.valueOf(costParams).getBytes(utf8); byte[] b64salt = b64encoder.encode(salt); byte[] b64hash = b64encoder.encode(hash); int size = (4 dollar.length) + params.length + b64salt.length + b64hash.length; ByteBuffer mcf = ByteBuffer.allocate(size); mcf.put(dollar).put(params); mcf.put(dollar).put(b64salt); mcf.put(dollar).put(b64hash); mcf.put(dollar); mcf.flip(); CharBuffer result = utf8.decode(mcf); Arrays.fill(hash, (byte) 0); Arrays.fill(salt, (byte) 0); Arrays.fill(b64hash, (byte) 0); Arrays.fill(b64salt, (byte) 0); Arrays.fill(mcf.array(), (byte) 0); return result; } /** * Checks a hash (as generated by the hash method) against a password. * * @param mcfHash The MCF formatted hash. * @param password The password. * * @return True if the password matches the hash, false if not. / public static boolean check(CharSequence mcfHash, CharSequence password) { Pattern regex = Pattern.compile("\\$(\\d+?)\\$(.+?)\\$(.+?)\\$"); Matcher matcher = regex.matcher(mcfHash); if (matcher.matches()) { int costParams = Integer.parseInt(matcher.group(1)); Base64.Decoder decoder = Base64.getDecoder(); byte[] salt = decoder.decode(matcher.group(2)); byte[] hash = decoder.decode(matcher.group(3)); int hN = 1 << (costParams >> 16); int hr = costParams >> 8 & 255; int hp = costParams & 255; byte[] cHash = hash(password, salt, hN, hr, hp, hash.length); for (int i = 0; i < cHash.length; i++) { if (cHash[i] != hash[i]) { return false; } } boolean result = MessageDigest.isEqual(cHash, hash); Arrays.fill(salt, (byte) 0); Arrays.fill(hash, (byte) 0); Arrays.fill(cHash, (byte) 0); return result; } else { throw new IllegalArgumentException("Hash is not in a recognisable format!"); } } static byte[] hash(CharSequence password, byte[] salt, int N, int r, int p, int dkLen) { return SCrypt.generate(toBytes(password), salt, N, r, p, dkLen); } private static byte[] salt() { try { byte[] salt = new byte[saltSize]; SecureRandom.getInstance("SHA1PRNG").nextBytes(salt); return salt; } catch (NoSuchAlgorithmException ex) { throw new IllegalStateException("SHA1PRNG not supported on this JVM!", ex); } } private static int log2(int operand) { double log2 = Math.log(operand) / Math.log(2); if (log2 % 1 != 0) { throw new IllegalArgumentException("N must be a power of 2."); } else { return Math.toIntExact(Math.round(log2)); } } / * Source: https://stackoverflow.com/a/9670279 / private static byte[] toBytes(CharSequence chars) { CharBuffer charBuffer = CharBuffer.wrap(chars); ByteBuffer byteBuffer = utf8.encode(charBuffer); byte[] bytes = Arrays.copyOfRange(byteBuffer.array(), byteBuffer.position(), byteBuffer.limit()); Arrays.fill(byteBuffer.array(), (byte) 0); return bytes; } } package helpers; import java.nio.ByteBuffer; import java.nio.CharBuffer; import java.nio.charset.Charset; import java.nio.charset.StandardCharsets; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import java.util.Arrays; import java.util.Base64; import java.util.regex.Matcher; import java.util.regex.Pattern; import org.bouncycastle.crypto.generators.SCrypt; /* * Wrapper for Bouncy Castle's scrypt implementation. * * Generates salted scrypt hashes in a format similar to Modular Crypt Format * (MCF). * * @author Mark George <mark.george@otago.ac.nz> / public final class ScryptHelper { // the standard work factors for scrypt private static final int N = 32768; private static final int r = 8; private static final int p = 1; private static final int saltSize = 64; private static final int dkLen = 64; private static final Charset utf8 = StandardCharsets.UTF_8; private ScryptHelper() { } /* * Generates an MCF-like formatted salted scrypt hash for the password. * * @param password The password to hash. * @return The MCF formatted hash. / public static CharBuffer hash(CharSequence password) { byte[] salt = salt(); byte[] hash = hash(password, salt, N, r, p, dkLen); Base64.Encoder b64encoder = Base64.getEncoder(); int costParams = (log2(N)) << 16 \| r << 8 \| p; byte[] dollar = "$".getBytes(utf8); byte[] params = String.valueOf(costParams).getBytes(utf8); byte[] b64salt = b64encoder.encode(salt); byte[] b64hash = b64encoder.encode(hash); int size = (4 dollar.length) + params.length + b64salt.length + b64hash.length; ByteBuffer mcf = ByteBuffer.allocate(size); mcf.put(dollar).put(params); mcf.put(dollar).put(b64salt); mcf.put(dollar).put(b64hash); mcf.put(dollar); mcf.flip(); CharBuffer result = utf8.decode(mcf); Arrays.fill(hash, (byte) 0); Arrays.fill(salt, (byte) 0); Arrays.fill(b64hash, (byte) 0); Arrays.fill(b64salt, (byte) 0); Arrays.fill(mcf.array(), (byte) 0); return result; } /** * Checks a hash (as generated by the hash method) against a password. * * @param mcfHash The MCF formatted hash. * @param password The password. * * @return True if the password matches the hash, false if not. / public static boolean check(CharSequence mcfHash, CharSequence password) { Pattern regex = Pattern.compile("\\$(\\d+?)\\$(.+?)\\$(.+?)\\$"); Matcher matcher = regex.matcher(mcfHash); if (matcher.matches()) { int costParams = Integer.parseInt(matcher.group(1)); Base64.Decoder decoder = Base64.getDecoder(); byte[] salt = decoder.decode(matcher.group(2)); byte[] hash = decoder.decode(matcher.group(3)); int hN = 1 << (costParams >> 16); int hr = costParams >> 8 & 255; int hp = costParams & 255; byte[] cHash = hash(password, salt, hN, hr, hp, hash.length); for (int i = 0; i < cHash.length; i++) { if (cHash[i] != hash[i]) { return false; } } Arrays.fill(salt, (byte) 0); Arrays.fill(hash, (byte) 0); Arrays.fill(cHash, (byte) 0); return true; } else { throw new IllegalArgumentException("Hash is not in a recognisable format!"); } } static byte[] hash(CharSequence password, byte[] salt, int N, int r, int p, int dkLen) { return SCrypt.generate(toBytes(password), salt, N, r, p, dkLen); } private static byte[] salt() { try { byte[] salt = new byte[saltSize]; SecureRandom.getInstance("SHA1PRNG").nextBytes(salt); return salt; } catch (NoSuchAlgorithmException ex) { throw new IllegalStateException("SHA1PRNG not supported on this JVM!", ex); } } private static int log2(int operand) { double log2 = Math.log(operand) / Math.log(2); if (log2 % 1 != 0) { throw new IllegalArgumentException("N must be a power of 2."); } else { return Math.toIntExact(Math.round(log2)); } } / * Source: https://stackoverflow.com/a/9670279 */ private static byte[] toBytes(CharSequence chars) { CharBuffer charBuffer = CharBuffer.wrap(chars); ByteBuffer byteBuffer = utf8.encode(charBuffer); byte[] bytes = Arrays.copyOfRange(byteBuffer.array(), byteBuffer.position(), byteBuffer.limit()); Arrays.fill(byteBuffer.array(), (byte) 0); return bytes; } }

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src/main/java/helpers/ScryptHelper.java

package helpers;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Base64;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.bouncycastle.crypto.generators.SCrypt;

/**
 * Wrapper for Bouncy Castle's scrypt implementation.
 *
 * Generates salted scrypt hashes in a format similar to Modular Crypt Format
 * (MCF).
 *
 * @author Mark George <mark.george@otago.ac.nz>
 */
public final class ScryptHelper {

// the standard work factors for scrypt
	private static final int N = 32768;
	private static final int r = 8;
	private static final int p = 1;

private static final int saltSize = 64;
	private static final int dkLen = 64;

private static final Charset utf8 = StandardCharsets.UTF_8;

private ScryptHelper() {
	}

/**
	 * Generates an MCF-like formatted salted scrypt hash for the password.
	 *
	 * @param password The password to hash.
	 * @return The MCF formatted hash.
	 */
	public static CharBuffer hash(CharSequence password) {
		byte[] salt = salt();
		byte[] hash = hash(password, salt, N, r, p, dkLen);

Base64.Encoder b64encoder = Base64.getEncoder();

int costParams = (log2(N)) << 16 | r << 8 | p;
		byte[] dollar = "$".getBytes(utf8);
		byte[] params = String.valueOf(costParams).getBytes(utf8);
		byte[] b64salt = b64encoder.encode(salt);
		byte[] b64hash = b64encoder.encode(hash);

int size = (4 * dollar.length) + params.length + b64salt.length + b64hash.length;

ByteBuffer mcf = ByteBuffer.allocate(size);
		mcf.put(dollar).put(params);
		mcf.put(dollar).put(b64salt);
		mcf.put(dollar).put(b64hash);
		mcf.put(dollar);
		mcf.flip();

CharBuffer result = utf8.decode(mcf);

Arrays.fill(hash, (byte) 0);
		Arrays.fill(salt, (byte) 0);
		Arrays.fill(b64hash, (byte) 0);
		Arrays.fill(b64salt, (byte) 0);
		Arrays.fill(mcf.array(), (byte) 0);

return result;
	}

/**
	 * Checks a hash (as generated by the hash method) against a password.
	 *
	 * @param mcfHash The MCF formatted hash.
	 * @param password The password.
	 *
	 * @return True if the password matches the hash, false if not.
	 */
	public static boolean check(CharSequence mcfHash, CharSequence password) {

Pattern regex = Pattern.compile("\\$(\\d+?)\\$(.+?)\\$(.+?)\\$");

Matcher matcher = regex.matcher(mcfHash);

if (matcher.matches()) {
			int costParams = Integer.parseInt(matcher.group(1));

Base64.Decoder decoder = Base64.getDecoder();

byte[] salt = decoder.decode(matcher.group(2));
			byte[] hash = decoder.decode(matcher.group(3));

int hN = 1 << (costParams >> 16);
			int hr = costParams >> 8 & 255;
			int hp = costParams & 255;

byte[] cHash = hash(password, salt, hN, hr, hp, hash.length);

for (int i = 0; i < cHash.length; i++) {
				if (cHash[i] != hash[i]) {
					return false;
				}
			}
			
			boolean result = MessageDigest.isEqual(cHash, hash);

Arrays.fill(salt, (byte) 0);
			Arrays.fill(hash, (byte) 0);
			Arrays.fill(cHash, (byte) 0);

return result;

} else {
			throw new IllegalArgumentException("Hash is not in a recognisable format!");
		}

}

static byte[] hash(CharSequence password, byte[] salt, int N, int r, int p, int dkLen) {
		return SCrypt.generate(toBytes(password), salt, N, r, p, dkLen);
	}

private static byte[] salt() {
		try {
			byte[] salt = new byte[saltSize];
			SecureRandom.getInstance("SHA1PRNG").nextBytes(salt);
			return salt;
		} catch (NoSuchAlgorithmException ex) {
			throw new IllegalStateException("SHA1PRNG not supported on this JVM!", ex);
		}
	}

private static int log2(int operand) {
		double log2 = Math.log(operand) / Math.log(2);
		if (log2 % 1 != 0) {
			throw new IllegalArgumentException("N must be a power of 2.");
		} else {
			return Math.toIntExact(Math.round(log2));
		}
	}

/*
	 * Source: https://stackoverflow.com/a/9670279
	 */
	private static byte[] toBytes(CharSequence chars) {
		CharBuffer charBuffer = CharBuffer.wrap(chars);
		ByteBuffer byteBuffer = utf8.encode(charBuffer);
		byte[] bytes = Arrays.copyOfRange(byteBuffer.array(), byteBuffer.position(), byteBuffer.limit());
		Arrays.fill(byteBuffer.array(), (byte) 0);
		return bytes;
	}

}

package helpers;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Base64;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.bouncycastle.crypto.generators.SCrypt;

// the standard work factors for scrypt
	private static final int N = 32768;
	private static final int r = 8;
	private static final int p = 1;

private static final int saltSize = 64;
	private static final int dkLen = 64;

private static final Charset utf8 = StandardCharsets.UTF_8;

private ScryptHelper() {
	}

Base64.Encoder b64encoder = Base64.getEncoder();

int size = (4 * dollar.length) + params.length + b64salt.length + b64hash.length;

ByteBuffer mcf = ByteBuffer.allocate(size);
		mcf.put(dollar).put(params);
		mcf.put(dollar).put(b64salt);
		mcf.put(dollar).put(b64hash);
		mcf.put(dollar);
		mcf.flip();

CharBuffer result = utf8.decode(mcf);

Arrays.fill(hash, (byte) 0);
		Arrays.fill(salt, (byte) 0);
		Arrays.fill(b64hash, (byte) 0);
		Arrays.fill(b64salt, (byte) 0);
		Arrays.fill(mcf.array(), (byte) 0);

return result;
	}

Pattern regex = Pattern.compile("\\$(\\d+?)\\$(.+?)\\$(.+?)\\$");

Matcher matcher = regex.matcher(mcfHash);

if (matcher.matches()) {
			int costParams = Integer.parseInt(matcher.group(1));

Base64.Decoder decoder = Base64.getDecoder();

byte[] salt = decoder.decode(matcher.group(2));
			byte[] hash = decoder.decode(matcher.group(3));

int hN = 1 << (costParams >> 16);
			int hr = costParams >> 8 & 255;
			int hp = costParams & 255;

byte[] cHash = hash(password, salt, hN, hr, hp, hash.length);

for (int i = 0; i < cHash.length; i++) {
				if (cHash[i] != hash[i]) {
					return false;
				}
			}

Arrays.fill(salt, (byte) 0);
			Arrays.fill(hash, (byte) 0);
			Arrays.fill(cHash, (byte) 0);

return true;

} else {
			throw new IllegalArgumentException("Hash is not in a recognisable format!");
		}

}

static byte[] hash(CharSequence password, byte[] salt, int N, int r, int p, int dkLen) {
		return SCrypt.generate(toBytes(password), salt, N, r, p, dkLen);
	}

}

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