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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"><title>Crypto++: elgamal.h Source File</title><link href="doxygen.css" rel="stylesheet" type="text/css"></head><body><!-- Generated by Doxygen 1.3.2 --><div class="qindex"><a class="qindex" href="index.html">Main Page</a> | <a class="qindex" href="namespaces.html">Namespace List</a> | <a class="qindex" href="hierarchy.html">Class Hierarchy</a> | <a class="qindex" href="classes.html">Alphabetical List</a> | <a class="qindex" href="annotated.html">Compound List</a> | <a class="qindex" href="files.html">File List</a> | <a class="qindex" href="namespacemembers.html">Namespace Members</a> | <a class="qindex" href="functions.html">Compound Members</a> | <a class="qindex" href="globals.html">File Members</a></div><h1>elgamal.h</h1><div class="fragment"><pre>00001 <span class="preprocessor">#ifndef CRYPTOPP_ELGAMAL_H</span>00002 <span class="preprocessor"></span><span class="preprocessor">#define CRYPTOPP_ELGAMAL_H</span>00003 <span class="preprocessor"></span>00004 <span class="preprocessor">#include "modexppc.h"</span>00005 <span class="preprocessor">#include "<a class="code" href="dsa_8h.html">dsa.h</a>"</span>00006 00007 NAMESPACE_BEGIN(CryptoPP)00008 00009 <span class="keyword">class </span>ElGamalBase : <span class="keyword">public</span> <a class="code" href="class_d_l___key_agreement_algorithm___d_h.html">DL_KeyAgreementAlgorithm_DH</a><Integer, NoCofactorMultiplication>, 00010 <span class="keyword">public</span> <a class="code" href="class_d_l___key_derivation_algorithm.html">DL_KeyDerivationAlgorithm</a><Integer>, 00011 <span class="keyword">public</span> <a class="code" href="class_d_l___symmetric_encryption_algorithm.html">DL_SymmetricEncryptionAlgorithm</a>00012 {00013 <span class="keyword">public</span>:00014 <span class="keywordtype">void</span> Derive(<span class="keyword">const</span> <a class="code" href="class_d_l___group_parameters.html">DL_GroupParameters<Integer></a> &params, byte *derivedKey, <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> derivedLength, <span class="keyword">const</span> <a class="code" href="class_integer.html">Integer</a> &agreedElement, <span class="keyword">const</span> <a class="code" href="class_integer.html">Integer</a> &ephemeralPublicKey)<span class="keyword"> const</span>00015 <span class="keyword"> </span>{00016 agreedElement.<a class="code" href="class_integer.html#_integerz39_1">Encode</a>(derivedKey, derivedLength);00017 }00018 00019 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> GetSymmetricKeyLength(<span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> plainTextLength)<span class="keyword"> const</span>00020 <span class="keyword"> </span>{00021 <span class="keywordflow">return</span> GetGroupParameters().GetModulus().ByteCount();00022 }00023 00024 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> GetSymmetricCiphertextLength(<span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> plainTextLength)<span class="keyword"> const</span>00025 <span class="keyword"> </span>{00026 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> len = GetGroupParameters().GetModulus().ByteCount();00027 <span class="keywordflow">if</span> (plainTextLength <= GetMaxSymmetricPlaintextLength(len))00028 <span class="keywordflow">return</span> len;00029 <span class="keywordflow">else</span>00030 <span class="keywordflow">return</span> 0;00031 }00032 00033 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> GetMaxSymmetricPlaintextLength(<span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> cipherTextLength)<span class="keyword"> const</span>00034 <span class="keyword"> </span>{00035 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> len = GetGroupParameters().GetModulus().ByteCount();00036 <span class="keywordflow">if</span> (cipherTextLength == len)00037 <span class="keywordflow">return</span> STDMIN(255U, len-3);00038 <span class="keywordflow">else</span>00039 <span class="keywordflow">return</span> 0;00040 }00041 00042 <span class="keywordtype">void</span> SymmetricEncrypt(<a class="code" href="class_random_number_generator.html">RandomNumberGenerator</a> &rng, <span class="keyword">const</span> byte *key, <span class="keyword">const</span> byte *plainText, <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> plainTextLength, byte *cipherText)<span class="keyword"> const</span>00043 <span class="keyword"> </span>{00044 <span class="keyword">const</span> <a class="code" href="class_integer.html">Integer</a> &p = GetGroupParameters().GetModulus();00045 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> modulusLen = p.<a class="code" href="class_integer.html#_integerz41_3">ByteCount</a>();00046 00047 <a class="code" href="class_sec_block.html">SecByteBlock</a> block(modulusLen-1);00048 rng.<a class="code" href="class_random_number_generator.html#_x917_r_n_ga4">GenerateBlock</a>(block, modulusLen-2-plainTextLength);00049 memcpy(block+modulusLen-2-plainTextLength, plainText, plainTextLength);00050 block[modulusLen-2] = plainTextLength;00051 00052 a_times_b_mod_c(<a class="code" href="class_integer.html">Integer</a>(key, modulusLen), <a class="code" href="class_integer.html">Integer</a>(block, modulusLen-1), p).<a class="code" href="class_integer.html#_integerz39_1">Encode</a>(cipherText, modulusLen);00053 }00054 00055 <a class="code" href="struct_decoding_result.html">DecodingResult</a> SymmetricDecrypt(<span class="keyword">const</span> byte *key, <span class="keyword">const</span> byte *cipherText, <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> cipherTextLength, byte *plainText)<span class="keyword"> const</span>00056 <span class="keyword"> </span>{00057 <span class="keyword">const</span> <a class="code" href="class_integer.html">Integer</a> &p = GetGroupParameters().GetModulus();00058 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> modulusLen = p.<a class="code" href="class_integer.html#_integerz41_3">ByteCount</a>();00059 00060 <span class="keywordflow">if</span> (cipherTextLength != modulusLen)00061 <span class="keywordflow">return</span> <a class="code" href="struct_decoding_result.html">DecodingResult</a>();00062 00063 <a class="code" href="class_integer.html">Integer</a> m = a_times_b_mod_c(<a class="code" href="class_integer.html">Integer</a>(cipherText, modulusLen), <a class="code" href="class_integer.html">Integer</a>(key, modulusLen).InverseMod(p), p);00064 00065 m.<a class="code" href="class_integer.html#_integerz39_1">Encode</a>(plainText, 1);00066 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> plainTextLength = plainText[0];00067 <span class="keywordflow">if</span> (plainTextLength > GetMaxSymmetricPlaintextLength(modulusLen))00068 <span class="keywordflow">return</span> <a class="code" href="struct_decoding_result.html">DecodingResult</a>();00069 m >>= 8;⌨️ 快捷键说明
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