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<div class="title">emsa2.cpp</div> </div>
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<div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="comment">// emsa2.cpp - written and placed in the public domain by Wei Dai</span>
<a name="l00002"></a>00002
<a name="l00003"></a>00003 <span class="preprocessor">#include "pch.h"</span>
<a name="l00004"></a>00004 <span class="preprocessor">#include "<a class="code" href="emsa2_8h.html" title="This file contains various padding schemes for public key algorithms.">emsa2.h</a>"</span>
<a name="l00005"></a>00005
<a name="l00006"></a>00006 <span class="preprocessor">#ifndef CRYPTOPP_IMPORTS</span>
<a name="l00007"></a>00007 <span class="preprocessor"></span>
<a name="l00008"></a>00008 NAMESPACE_BEGIN(CryptoPP)
<a name="l00009"></a>00009
<a name="l00010"></a>00010 void <a class="code" href="class_e_m_s_a2_pad.html" title="_">EMSA2Pad</a>::ComputeMessageRepresentative(<a class="code" href="class_random_number_generator.html" title="interface for random number generators">RandomNumberGenerator</a> &rng,
<a name="l00011"></a>00011 const byte *recoverableMessage, <span class="keywordtype">size_t</span> recoverableMessageLength,
<a name="l00012"></a>00012 <a class="code" href="class_hash_transformation.html" title="interface for hash functions and data processing part of MACs">HashTransformation</a> &hash, HashIdentifier hashIdentifier, <span class="keywordtype">bool</span> messageEmpty,
<a name="l00013"></a>00013 byte *representative, <span class="keywordtype">size_t</span> representativeBitLength)<span class="keyword"> const</span>
<a name="l00014"></a>00014 <span class="keyword"></span>{
<a name="l00015"></a>00015 assert(representativeBitLength >= MinRepresentativeBitLength(hashIdentifier.second, hash.DigestSize()));
<a name="l00016"></a>00016
<a name="l00017"></a>00017 <span class="keywordflow">if</span> (representativeBitLength % 8 != 7)
<a name="l00018"></a>00018 <span class="keywordflow">throw</span> <a class="code" href="class_p_k___signature_scheme_1_1_invalid_key_length.html" title="invalid key exception, may be thrown by any function in this class if the private or public key has a...">PK_SignatureScheme::InvalidKeyLength</a>(<span class="stringliteral">"EMSA2: EMSA2 requires a key length that is a multiple of 8"</span>);
<a name="l00019"></a>00019
<a name="l00020"></a>00020 <span class="keywordtype">size_t</span> digestSize = hash.DigestSize();
<a name="l00021"></a>00021 <span class="keywordtype">size_t</span> representativeByteLength = BitsToBytes(representativeBitLength);
<a name="l00022"></a>00022
<a name="l00023"></a>00023 representative[0] = messageEmpty ? 0x4b : 0x6b;
<a name="l00024"></a>00024 memset(representative+1, 0xbb, representativeByteLength-digestSize-4); <span class="comment">// pad with 0xbb</span>
<a name="l00025"></a>00025 byte *afterP2 = representative+representativeByteLength-digestSize-3;
<a name="l00026"></a>00026 afterP2[0] = 0xba;
<a name="l00027"></a>00027 hash.Final(afterP2+1);
<a name="l00028"></a>00028 representative[representativeByteLength-2] = *hashIdentifier.first;
<a name="l00029"></a>00029 representative[representativeByteLength-1] = 0xcc;
<a name="l00030"></a>00030 }
<a name="l00031"></a>00031
<a name="l00032"></a>00032 NAMESPACE_END
<a name="l00033"></a>00033
<a name="l00034"></a>00034 <span class="preprocessor">#endif</span>
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