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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html;charset=UTF-8"><title>Crypto++: elgamal.h Source File</title><link href="doxygen.css" rel="stylesheet" type="text/css"><link href="tabs.css" rel="stylesheet" type="text/css"></head><body><!-- Generated by Doxygen 1.5.2 --><div class="tabs"> <ul> <li><a href="index.html"><span>Main Page</span></a></li> <li><a href="namespaces.html"><span>Namespaces</span></a></li> <li><a href="classes.html"><span>Classes</span></a></li> <li class="current"><a href="files.html"><span>Files</span></a></li> </ul></div><div class="tabs"> <ul> <li><a href="files.html"><span>File List</span></a></li> <li><a href="globals.html"><span>File Members</span></a></li> </ul></div><h1>elgamal.h</h1><div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="preprocessor">#ifndef CRYPTOPP_ELGAMAL_H</span><a name="l00002"></a>00002 <span class="preprocessor"></span><span class="preprocessor">#define CRYPTOPP_ELGAMAL_H</span><a name="l00003"></a>00003 <span class="preprocessor"></span><a name="l00004"></a>00004 <span class="preprocessor">#include "modexppc.h"</span><a name="l00005"></a>00005 <span class="preprocessor">#include "<a class="code" href="dsa_8h.html">dsa.h</a>"</span><a name="l00006"></a>00006 <a name="l00007"></a>00007 NAMESPACE_BEGIN(CryptoPP)<a name="l00008"></a>00008 <a name="l00009"></a><a class="code" href="class_el_gamal_base.html">00009</a> class CRYPTOPP_NO_VTABLE <a class="code" href="class_el_gamal_base.html">ElGamalBase</a> : public <a class="code" href="class_d_l___key_agreement_algorithm___d_h.html" title="DH key agreement algorithm.">DL_KeyAgreementAlgorithm_DH</a><<a class="code" href="class_integer.html" title="multiple precision integer and basic arithmetics">Integer</a>, <a class="code" href="struct_enum_to_type.html">NoCofactorMultiplication</a>>, <a name="l00010"></a>00010 public <a class="code" href="class_d_l___key_derivation_algorithm.html" title="interface for key derivation algorithms used in DL cryptosystems">DL_KeyDerivationAlgorithm</a><Integer>, <a name="l00011"></a>00011 public <a class="code" href="class_d_l___symmetric_encryption_algorithm.html" title="interface for symmetric encryption algorithms used in DL cryptosystems">DL_SymmetricEncryptionAlgorithm</a><a name="l00012"></a>00012 {<a name="l00013"></a>00013 <span class="keyword">public</span>:<a name="l00014"></a><a class="code" href="class_el_gamal_base.html#aeac8cd47a26c15417fe6cb30af8ae0f">00014</a> <span class="keywordtype">void</span> Derive(<span class="keyword">const</span> <a class="code" href="class_d_l___group_parameters.html" title="interface for DL group parameters">DL_GroupParameters<Integer></a> &groupParams, byte *derivedKey, <span class="keywordtype">size_t</span> derivedLength, <span class="keyword">const</span> Integer &agreedElement, <span class="keyword">const</span> Integer &ephemeralPublicKey, <span class="keyword">const</span> <a class="code" href="class_name_value_pairs.html" title="interface for retrieving values given their names">NameValuePairs</a> &derivationParams)<span class="keyword"> const</span><a name="l00015"></a>00015 <span class="keyword"> </span>{<a name="l00016"></a>00016 agreedElement.<a class="code" href="class_integer.html#c12ea467de9a609b86ec03d8cb8837e4" title="encode in big-endian format">Encode</a>(derivedKey, derivedLength);<a name="l00017"></a>00017 }<a name="l00018"></a>00018 <a name="l00019"></a><a class="code" href="class_el_gamal_base.html#14ac7ac4ccb1d1bf5221e679ab24c28d">00019</a> <span class="keywordtype">size_t</span> GetSymmetricKeyLength(<span class="keywordtype">size_t</span> plainTextLength)<span class="keyword"> const</span><a name="l00020"></a>00020 <span class="keyword"> </span>{<a name="l00021"></a>00021 <span class="keywordflow">return</span> GetGroupParameters().GetModulus().ByteCount();<a name="l00022"></a>00022 }<a name="l00023"></a>00023 <a name="l00024"></a><a class="code" href="class_el_gamal_base.html#8598d1ce1f20423ae10dd8ff80e2cfd3">00024</a> <span class="keywordtype">size_t</span> GetSymmetricCiphertextLength(<span class="keywordtype">size_t</span> plainTextLength)<span class="keyword"> const</span><a name="l00025"></a>00025 <span class="keyword"> </span>{<a name="l00026"></a>00026 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> len = GetGroupParameters().GetModulus().ByteCount();<a name="l00027"></a>00027 <span class="keywordflow">if</span> (plainTextLength <= GetMaxSymmetricPlaintextLength(len))<a name="l00028"></a>00028 <span class="keywordflow">return</span> len;<a name="l00029"></a>00029 <span class="keywordflow">else</span><a name="l00030"></a>00030 <span class="keywordflow">return</span> 0;<a name="l00031"></a>00031 }<a name="l00032"></a>00032 <a name="l00033"></a><a class="code" href="class_el_gamal_base.html#cab5ed17e036c9be22d3c7db612cd51e">00033</a> <span class="keywordtype">size_t</span> GetMaxSymmetricPlaintextLength(<span class="keywordtype">size_t</span> cipherTextLength)<span class="keyword"> const</span><a name="l00034"></a>00034 <span class="keyword"> </span>{<a name="l00035"></a>00035 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> len = GetGroupParameters().GetModulus().ByteCount();<a name="l00036"></a>00036 <span class="keywordflow">if</span> (cipherTextLength == len)<a name="l00037"></a>00037 <span class="keywordflow">return</span> STDMIN(255U, len-3);<a name="l00038"></a>00038 <span class="keywordflow">else</span><a name="l00039"></a>00039 <span class="keywordflow">return</span> 0;<a name="l00040"></a>00040 }<a name="l00041"></a>00041 <a name="l00042"></a><a class="code" href="class_el_gamal_base.html#4b842a714cf952f690e33a1c3b9c718b">00042</a> <span class="keywordtype">void</span> SymmetricEncrypt(<a class="code" href="class_random_number_generator.html" title="interface for random number generators">RandomNumberGenerator</a> &rng, <span class="keyword">const</span> byte *key, <span class="keyword">const</span> byte *plainText, <span class="keywordtype">size_t</span> plainTextLength, byte *cipherText, <span class="keyword">const</span> <a class="code" href="class_name_value_pairs.html" title="interface for retrieving values given their names">NameValuePairs</a> &parameters)<span class="keyword"> const</span><a name="l00043"></a>00043 <span class="keyword"> </span>{<a name="l00044"></a>00044 <span class="keyword">const</span> Integer &p = GetGroupParameters().GetModulus();<a name="l00045"></a>00045 <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> modulusLen = p.<a class="code" href="class_integer.html#e7ee3f1bbea2b3138c6d8f1ce1aa2bf9" title="number of significant bytes = ceiling(BitCount()/8)">ByteCount</a>();<a name="l00046"></a>00046 <a name="l00047"></a>00047 <a class="code" href="class_sec_block.html" title="a block of memory allocated using A">SecByteBlock</a> block(modulusLen-1);<a name="l00048"></a>00048 rng.<a class="code" href="class_random_number_generator.html#497145546d24e6d4abaf10b7e0f1ba17" title="generate random array of bytes">GenerateBlock</a>(block, modulusLen-2-plainTextLength);<a name="l00049"></a>00049 memcpy(block+modulusLen-2-plainTextLength, plainText, plainTextLength);<a name="l00050"></a>00050 block[modulusLen-2] = (byte)plainTextLength;<a name="l00051"></a>00051 <a name="l00052"></a>00052 a_times_b_mod_c(Integer(key, modulusLen), Integer(block, modulusLen-1), p).<a class="code" href="class_integer.html#c12ea467de9a609b86ec03d8cb8837e4" title="encode in big-endian format">Encode</a>(cipherText, modulusLen);<a name="l00053"></a>00053 }⌨️ 快捷键说明
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