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