package gnu.crypto.sig.rsa;
// ----------------------------------------------------------------------------
// $Id: EMSA_PSS.java,v 1.8 2005/10/06 04:24:18 rsdio Exp $
//
// Copyright (C) 2001, 2002, 2003 Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.
//
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
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// along with this program; see the file COPYING. If not, write to the
//
// Free Software Foundation Inc.,
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// Boston, MA 02110-1301
// USA
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library. Thus, the terms and
// conditions of the GNU General Public License cover the whole
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// ----------------------------------------------------------------------------
import gnu.crypto.hash.HashFactory;
import gnu.crypto.hash.IMessageDigest;
import gnu.crypto.util.Util;
import java.io.PrintWriter;
import java.util.Arrays;
/**
* <p>An implementation of the EMSA-PSS encoding/decoding scheme.</p>
*
* <p>EMSA-PSS coincides with EMSA4 in IEEE P1363a D5 except that EMSA-PSS acts
* on octet strings and not on bit strings. In particular, the bit lengths of
* the hash and the salt must be multiples of 8 in EMSA-PSS. Moreover, EMSA4
* outputs an integer of a desired bit length rather than an octet string.</p>
*
* <p>EMSA-PSS is parameterized by the choice of hash function Hash and mask
* generation function MGF. In this submission, MGF is based on a Hash
* definition that coincides with the corresponding definitions in IEEE Std
* 1363-2000, PKCS #1 v2.0, and the draft ANSI X9.44. In PKCS #1 v2.0 and the
* draft ANSI X9.44, the recommended hash function is SHA-1, while IEEE Std
* 1363-2000 recommends SHA-1 and RIPEMD-160.</p>
*
* <p>References:</p>
* <ol>
* <li><a href="http://www.cosic.esat.kuleuven.ac.be/nessie/workshop/submissions/rsa-pss.zip">
* RSA-PSS Signature Scheme with Appendix, part B.</a><br>
* Primitive specification and supporting documentation.<br>
* Jakob Jonsson and Burt Kaliski.</li>
* </ol>
*
* @version $Revision: 1.8 $
*/
public class EMSA_PSS implements Cloneable {
// Debugging methods and variables
// -------------------------------------------------------------------------
private static final String NAME = "emsa-pss";
private static final boolean DEBUG = false;
private static final int debuglevel = 5;
private static final PrintWriter err = new PrintWriter(System.out, true);
private static void debug(String s) {
err.println(">>> "+NAME+": "+s);
}
// Constants and variables
// -------------------------------------------------------------------------
/** The underlying hash function to use with this instance. */
private IMessageDigest hash;
/** The output size of the hash function in octets. */
private int hLen;
// Constructor(s)
// -------------------------------------------------------------------------
/**
* <p>Trivial private constructor to enforce use through Factory method.</p>
*
* @param hash the message digest instance to use with this scheme instance.
*/
private EMSA_PSS(IMessageDigest hash) {
super();
this.hash = hash;
hLen = hash.hashSize();
}
// Class methods
// -------------------------------------------------------------------------
/**
* <p>Returns an instance of this object given a designated name of a hash
* function.</p>
*
* @param mdName the canonical name of a hash function.
* @return an instance of this object configured for use with the designated
* options.
*/
public static EMSA_PSS getInstance(String mdName) {
IMessageDigest hash = HashFactory.getInstance(mdName);
return new EMSA_PSS(hash);
}
// Instance methods
// -------------------------------------------------------------------------
// Cloneable interface implementation --------------------------------------
public Object clone() {
return getInstance(hash.name());
}
// own methods -------------------------------------------------------------
/**
* <p>The encoding operation EMSA-PSS-Encode computes the hash of a message
* <code>M</code> using a hash function and maps the result to an encoded
* message <code>EM</code> of a specified length using a mask generation
* function.</p>
*
* @param mHash the byte sequence resulting from applying the message digest
* algorithm Hash to the message <i>M</i>.
* @param emBits the maximal bit length of the integer OS2IP(EM), at least
* <code>8.hLen + 8.sLen + 9</code>.
* @param salt the salt to use when encoding the output.
* @return the encoded message <code>EM</code>, an octet string of length
* <code>emLen = CEILING(emBits / 8)</code>.
* @exception IllegalArgumentException if an exception occurs.
*
*/
public byte[] encode(byte[] mHash, int emBits, byte[] salt) {
int sLen = salt.length;
// 1. If the length of M is greater than the input limitation for the hash
// function (2**61 - 1 octets for SHA-1) then output "message too long"
// and stop.
// 2. Let mHash = Hash(M), an octet string of length hLen.
if (hLen != mHash.length) {
throw new IllegalArgumentException("wrong hash");
}
// 3. If emBits < 8.hLen + 8.sLen + 9, output 'encoding error' and stop.
if (emBits < (8*hLen + 8*sLen + 9)) {
throw new IllegalArgumentException("encoding error");
}
int emLen = (emBits + 7) / 8;
// 4. Generate a random octet string salt of length sLen; if sLen = 0,
// then salt is the empty string.
// ...passed as argument to accomodate JCE
// 5. Let M0 = 00 00 00 00 00 00 00 00 || mHash || salt;
// M0 is an octet string of length 8 + hLen + sLen with eight initial zero
// octets.
// 6. Let H = Hash(M0), an octet string of length hLen.
byte[] H;
int i;
synchronized (hash) {
for (i = 0; i < 8; i++) {
hash.update((byte) 0x00);
}
hash.update(mHash, 0, hLen);
hash.update(salt, 0, sLen);
H = hash.digest();
}
// 7. Generate an octet string PS consisting of emLen - sLen - hLen - 2
// zero octets. The length of PS may be 0.
// 8. Let DB = PS || 01 || salt.
byte[] DB = new byte[emLen - sLen - hLen - 2 + 1 + sLen];
DB[emLen - sLen - hLen - 2] = 0x01;
System.arraycopy(salt, 0, DB, emLen - sLen - hLen - 1, sLen);
// 9. Let dbMask = MGF(H, emLen - hLen - 1).
byte[] dbMask = MGF(H, emLen - hLen - 1);
if (DEBUG && debuglevel > 8) {
debug("dbMask (encode): "+Util.toString(dbMask));
debug("DB (encode): "+Util.toString(DB));
}
// 10. Let maskedDB = DB XOR dbMask.
for (i = 0; i < DB.length; i++) {
DB[i] = (byte)(DB[i] ^ dbMask[i]);
}
// 11. Set the leftmost 8emLen - emBits bits of the leftmost octet in
// maskedDB to zero.
DB[0] &= (0xFF >>> (8*emLen - emBits));
// 12. Let EM = maskedDB || H || bc, where bc is the single octet with
// hexadecimal value 0xBC.
byte[] result = new byte[emLen];
System.arraycopy(DB, 0, result, 0, emLen - hLen - 1);
System.arraycopy(H, 0, result, emLen - hLen - 1, hLen);
result[emLen - 1] = (byte) 0xBC;
// 13. Output EM.
return result;
}
/**
* <p>The decoding operation EMSA-PSS-Decode recovers the message hash from
* an encoded message <code>EM</code> and compares it to the hash of
* <code>M</code>.</p>
*
* @param mHash the byte sequence resulting from applying the message digest
* algorithm Hash to the message <i>M</i>.
* @param EM the <i>encoded message</i>, an octet string of length
* <code>emLen = CEILING(emBits/8).
* @param emBits the maximal bit length of the integer OS2IP(EM), at least
* <code>8.hLen + 8.sLen + 9</code>.
* @param sLen the length, in octets, of the expected salt.
* @return <code>true</code> if the result of the verification was
* <i>consistent</i> with the expected reseult; and <code>false</code> if the
* result was <i>inconsistent</i>.
* @exception IllegalArgumentException if an exception occurs.
*/
public boolean decode(byte[] mHash, byte[] EM, int emBits, int sLen) {
if (DEBUG && debuglevel > 8) {
debug("mHash: "+Util.toString(mHash));
debug("EM: "+Util.toString(EM));
debug("emBits: "+String.valueOf(emBits));
debug("sLen: "+String.valueOf(sLen));
}
if (sLen < 0) {
throw new IllegalArgumentException("sLen");
}
// 1. If the length of M is greater than the input limitation for the hash
// function (2**61 ? 1 octets for SHA-1) then output 'inconsistent' and
// stop.
// 2. Let mHash = Hash(M), an octet string of length hLen.
if (hLen != mHash.length) {
if (DEBUG && debuglevel > 8) {
debug("hLen != mHash.length; hLen: "+String.valueOf(hLen));
}
throw new IllegalArgumentException("wrong hash");
}
// 3. If emBits < 8.hLen + 8.sLen + 9, output 'decoding error' and stop.
if (emBits < (8*hLen + 8*sLen + 9)) {
if (DEBUG && debuglevel > 8) {
debug("emBits < (8hLen + 8sLen + 9); sLen: "+String.valueOf(sLen));
}
throw new IllegalArgumentException("decoding error");
}
int emLen = (emBits + 7) / 8;
// 4. If the rightmost octet of EM does not have hexadecimal value bc,
// output 'inconsistent' and stop.
if ((EM[EM.length - 1] & 0xFF) != 0xBC) {
if (DEBUG && debuglevel > 8) {
debug("EM does not end with 0xBC");
}
return false;
}
// 5. Let maskedDB be the leftmost emLen ? hLen ? 1 octets of EM, and let
// H be the next hLen octets.
// 6. If the leftmost 8.emLen ? emBits bits of the leftmost octet in
// maskedDB are not all equal to zero, output 'inconsistent' and stop.
if ((EM[0] & (0xFF << (8 - (8*emLen - emBits)))) != 0) {
if (DEBUG && debuglevel > 8) {
debug("Leftmost 8emLen - emBits bits of EM are not 0s");
}
return false;
}
byte[] DB = new byte[emLen - hLen - 1];
byte[] H = new byte[hLen];
System.arraycopy(EM, 0, DB, 0, emLen - hLen - 1);
System.arraycopy(EM, emLen - hLen - 1, H, 0, hLen);
// 7. Let dbMask = MGF(H, emLen ? hLen ? 1).
byte[] dbMask = MGF(H, emLen - hLen - 1);
// 8. Let DB = maskedDB XOR dbMask.
int i;
for (i = 0; i < DB.length; i++) {
DB[i] = (byte)(DB[i] ^ dbMask[i]);
}
// 9. Set the leftmost 8.emLen ? emBits bits of DB to zero.
DB[0] &= (0xFF >>> (8*emLen - emBits));
if (DEBUG && debuglevel > 8) {
debug("dbMask (decode): "+Util.toString(dbMask));
debug("DB (decode): "+Util.toString(DB));
}
// 10. If the emLen -hLen -sLen -2 leftmost octets of DB are not zero or
// if the octet at position emLen -hLen -sLen -1 is not equal to 0x01,
// output 'inconsistent' and stop.
// IMPORTANT (rsn): this is an error in the specs, the index of the 0x01
// byte should be emLen -hLen -sLen -2 and not -1! authors have been
// advised
for (i = 0; i < (emLen - hLen - sLen - 2); i++) {
if (DB[i] != 0) {
if (DEBUG && debuglevel > 8) {
debug("DB["+String.valueOf(i)+"] != 0x00");
}
return false;
}
}
if (DB[i] != 0x01) { // i == emLen -hLen -sLen -2
if (DEBUG && debuglevel > 8) {
debug("DB's byte at position (emLen -hLen -sLen -2); i.e. "
+String.valueOf(i)+" is not 0x01");
}
return false;
}
// 11. Let salt be the last sLen octets of DB.
byte[] salt = new byte[sLen];
System.arraycopy(DB, DB.length - sLen, salt, 0, sLen);
// 12. Let M0 = 00 00 00 00 00 00 00 00 || mHash || salt;
// M0 is an octet string of length 8 + hLen + sLen with eight initial
// zero octets.
// 13. Let H0 = Hash(M0), an octet string of length hLen.
byte[] H0;
synchronized (hash) {
for (i = 0; i < 8; i++) {
hash.update((byte) 0x00);
}
hash.update(mHash, 0, hLen);
hash.update(salt, 0, sLen);
H0 = hash.digest();
}
// 14. If H = H0, output 'consistent.' Otherwise, output 'inconsistent.'
return Arrays.equals(H, H0);
}
// helper methods ----------------------------------------------------------
/**
* <p>A mask generation function takes an octet string of variable length
* and a desired output length as input, and outputs an octet string of the
* desired length. There may be restrictions on the length of the input and
* output octet strings, but such bounds are generally very large. Mask
* generation functions are deterministic; the octet string output is
* completely determined by the input octet string. The output of a mask
* generation function should be pseudorandom, that is, it should be
* infeasible to predict, given one part of the output but not the input,
* another part of the output. The provable security of RSA-PSS relies on
* the random nature of the output of the mask generation function, which in
* turn relies on the random nature of the underlying hash function.</p>
*
* @param Z a seed.
* @param l the desired output length in octets.
* @return the mask.
* @exception IllegalArgumentException if the desired output length is too
* long.
*/
private byte[] MGF(byte[] Z, int l) {
// 1. If l > (2**32).hLen, output 'mask too long' and stop.
if (l < 1 || (l & 0xFFFFFFFFL) > ((hLen & 0xFFFFFFFFL) << 32L)) {
throw new IllegalArgumentException("mask too long");
}
// 2. Let T be the empty octet string.
byte[] result = new byte[l];
// 3. For i = 0 to CEILING(l/hLen) ? 1, do
int limit = ((l + hLen - 1) / hLen) - 1;
IMessageDigest hashZ = null;
hashZ = (IMessageDigest) hash.clone();
hashZ.digest();
hashZ.update(Z, 0, Z.length);
IMessageDigest hashZC = null;
byte[] t;
int sofar = 0;
int length;
for (int i = 0; i < limit; i++) {
// 3.1 Convert i to an octet string C of length 4 with the primitive
// I2OSP: C = I2OSP(i, 4).
// 3.2 Concatenate the hash of the seed Z and C to the octet string T:
// T = T || Hash(Z || C)
hashZC = (IMessageDigest) hashZ.clone();
hashZC.update((byte)(i >>> 24));
hashZC.update((byte)(i >>> 16));
hashZC.update((byte)(i >>> 8));
hashZC.update((byte) i );
t = hashZC.digest();
length = l - sofar;
length = (length > hLen ? hLen : length);
System.arraycopy(t, 0, result, sofar, length);
sofar += length;
}
// 4. Output the leading l octets of T as the octet string mask.
return result;
}
}