1 files changed, 146 insertions, 0 deletions
diff --git a/lib/pk_pad/emsa4/emsa4.cpp b/lib/pk_pad/emsa4/emsa4.cpp
new file mode 100644
index 000000000..c8b8cbc6a
--- /dev/null
+++ b/lib/pk_pad/emsa4/emsa4.cpp
@@ -0,0 +1,146 @@
+/*
+* EMSA4
+* (C) 1999-2007 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/emsa4.h>
+#include <botan/mgf1.h>
+#include <botan/internal/bit_ops.h>
+
+namespace Botan {
+
+/*
+* EMSA4 Update Operation
+*/
+void EMSA4::update(const byte input[], size_t length)
+   {
+   hash->update(input, length);
+   }
+
+/*
+* Return the raw (unencoded) data
+*/
+secure_vector<byte> EMSA4::raw_data()
+   {
+   return hash->final();
+   }
+
+/*
+* EMSA4 Encode Operation
+*/
+secure_vector<byte> EMSA4::encoding_of(const secure_vector<byte>& msg,
+                                      size_t output_bits,
+                                      RandomNumberGenerator& rng)
+   {
+   const size_t HASH_SIZE = hash->output_length();
+
+   if(msg.size() != HASH_SIZE)
+      throw Encoding_Error("EMSA4::encoding_of: Bad input length");
+   if(output_bits < 8*HASH_SIZE + 8*SALT_SIZE + 9)
+      throw Encoding_Error("EMSA4::encoding_of: Output length is too small");
+
+   const size_t output_length = (output_bits + 7) / 8;
+
+   secure_vector<byte> salt = rng.random_vec(SALT_SIZE);
+
+   for(size_t j = 0; j != 8; ++j)
+      hash->update(0);
+   hash->update(msg);
+   hash->update(salt);
+   secure_vector<byte> H = hash->final();
+
+   secure_vector<byte> EM(output_length);
+
+   EM[output_length - HASH_SIZE - SALT_SIZE - 2] = 0x01;
+   buffer_insert(EM, output_length - 1 - HASH_SIZE - SALT_SIZE, salt);
+   mgf->mask(&H[0], HASH_SIZE, &EM[0], output_length - HASH_SIZE - 1);
+   EM[0] &= 0xFF >> (8 * ((output_bits + 7) / 8) - output_bits);
+   buffer_insert(EM, output_length - 1 - HASH_SIZE, H);
+   EM[output_length-1] = 0xBC;
+
+   return EM;
+   }
+
+/*
+* EMSA4 Decode/Verify Operation
+*/
+bool EMSA4::verify(const secure_vector<byte>& const_coded,
+                   const secure_vector<byte>& raw, size_t key_bits)
+   {
+   const size_t HASH_SIZE = hash->output_length();
+   const size_t KEY_BYTES = (key_bits + 7) / 8;
+
+   if(key_bits < 8*HASH_SIZE + 9)
+      return false;
+
+   if(raw.size() != HASH_SIZE)
+      return false;
+
+   if(const_coded.size() > KEY_BYTES || const_coded.size() <= 1)
+      return false;
+
+   if(const_coded[const_coded.size()-1] != 0xBC)
+      return false;
+
+   secure_vector<byte> coded = const_coded;
+   if(coded.size() < KEY_BYTES)
+      {
+      secure_vector<byte> temp(KEY_BYTES);
+      buffer_insert(temp, KEY_BYTES - coded.size(), coded);
+      coded = temp;
+      }
+
+   const size_t TOP_BITS = 8 * ((key_bits + 7) / 8) - key_bits;
+   if(TOP_BITS > 8 - high_bit(coded[0]))
+      return false;
+
+   byte* DB = &coded[0];
+   const size_t DB_size = coded.size() - HASH_SIZE - 1;
+
+   const byte* H = &coded[DB_size];
+   const size_t H_size = HASH_SIZE;
+
+   mgf->mask(&H[0], H_size, &DB[0], DB_size);
+   DB[0] &= 0xFF >> TOP_BITS;
+
+   size_t salt_offset = 0;
+   for(size_t j = 0; j != DB_size; ++j)
+      {
+      if(DB[j] == 0x01)
+         { salt_offset = j + 1; break; }
+      if(DB[j])
+         return false;
+      }
+   if(salt_offset == 0)
+      return false;
+
+   for(size_t j = 0; j != 8; ++j)
+      hash->update(0);
+   hash->update(raw);
+   hash->update(&DB[salt_offset], DB_size - salt_offset);
+   secure_vector<byte> H2 = hash->final();
+
+   return same_mem(&H[0], &H2[0], HASH_SIZE);
+   }
+
+/*
+* EMSA4 Constructor
+*/
+EMSA4::EMSA4(HashFunction* h) :
+   SALT_SIZE(h->output_length()), hash(h)
+   {
+   mgf = new MGF1(hash->clone());
+   }
+
+/*
+* EMSA4 Constructor
+*/
+EMSA4::EMSA4(HashFunction* h, size_t salt_size) :
+   SALT_SIZE(salt_size), hash(h)
+   {
+   mgf = new MGF1(hash->clone());
+   }
+
+}