1 /* 2 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package sun.security.rsa; 26 27 import java.security.*; 28 29 /** 30 * This class implements the MGF1 mask generation function defined in PKCS#1 31 * v2.2 B.2.1. A mask generation function takes an octet string of variable 32 * length and a desired output length as input and outputs an octet string of 33 * the desired length. MGF1 is a mask generation function based on a hash 34 * function, i.e. message digest algorithm. 35 * 36 * @since 11 37 */ 38 public final class MGF1 { 39 40 private final MessageDigest md; 41 42 /** 43 * Construct an instance of MGF1 based on the specified digest algorithm. 44 */ 45 MGF1(String mdAlgo) throws NoSuchAlgorithmException { 46 this.md = MessageDigest.getInstance(mdAlgo); 47 } 48 49 /** 50 * Using the specified seed bytes, generate the mask, xor the mask 51 * with the specified output buffer and store the result into the 52 * output buffer (essentially replaced in place). 53 * 54 * @param seed the buffer holding the seed bytes 55 * @param seedOfs the index of the seed bytes 56 * @param seedLen the length of the seed bytes to be used by MGF1 57 * @param maskLen the intended length of the generated mask 58 * @param out the output buffer holding the mask 59 * @param outOfs the index of the output buffer for the mask 60 */ 61 void generateAndXor(byte[] seed, int seedOfs, int seedLen, int maskLen, 62 byte[] out, int outOfs) throws RuntimeException { 63 byte[] C = new byte[4]; // 32 bit counter 64 byte[] digest = new byte[md.getDigestLength()]; 65 while (maskLen > 0) { 66 md.update(seed, seedOfs, seedLen); 67 md.update(C); 68 try { 69 md.digest(digest, 0, digest.length); 70 } catch (DigestException e) { 71 // should never happen 72 throw new RuntimeException(e.toString()); 73 } 74 for (int i = 0; (i < digest.length) && (maskLen > 0); maskLen--) { 75 out[outOfs++] ^= digest[i++]; 76 } 77 if (maskLen > 0) { 78 // increment counter 79 for (int i = C.length - 1; (++C[i] == 0) && (i > 0); i--) { 80 // empty 81 } 82 } 83 } 84 } 85 86 /** 87 * Returns the name of this MGF1 instance, i.e. "MGF1" followed by the 88 * digest algorithm it based on. 89 */ 90 String getName() { 91 return "MGF1" + md.getAlgorithm(); 92 } 93 }