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/*
* X9.42 PRF
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/prf_x942.h>
#include <botan/der_enc.h>
#include <botan/oids.h>
#include <botan/sha160.h>
#include <botan/loadstor.h>
#include <algorithm>
#include <memory>
namespace Botan {
namespace {
/*
* Encode an integer as an OCTET STRING
*/
MemoryVector<byte> encode_x942_int(u32bit n)
{
byte n_buf[4] = { 0 };
store_be(n, n_buf);
return DER_Encoder().encode(n_buf, 4, OCTET_STRING).get_contents();
}
}
/*
* X9.42 PRF
*/
SecureVector<byte> X942_PRF::derive(size_t key_len,
const byte secret[], size_t secret_len,
const byte salt[], size_t salt_len) const
{
SHA_160 hash;
const OID kek_algo(key_wrap_oid);
SecureVector<byte> key;
u32bit counter = 1;
while(key.size() != key_len && counter)
{
hash.update(secret, secret_len);
hash.update(
DER_Encoder().start_cons(SEQUENCE)
.start_cons(SEQUENCE)
.encode(kek_algo)
.raw_bytes(encode_x942_int(counter))
.end_cons()
.encode_if(salt_len != 0,
DER_Encoder()
.start_explicit(0)
.encode(salt, salt_len, OCTET_STRING)
.end_explicit()
)
.start_explicit(2)
.raw_bytes(encode_x942_int(static_cast<u32bit>(8 * key_len)))
.end_explicit()
.end_cons().get_contents()
);
SecureVector<byte> digest = hash.final();
const size_t needed = std::min(digest.size(), key_len - key.size());
key += std::make_pair(&digest[0], needed);
++counter;
}
return key;
}
/*
* X9.42 Constructor
*/
X942_PRF::X942_PRF(const std::string& oid)
{
if(OIDS::have_oid(oid))
key_wrap_oid = OIDS::lookup(oid).as_string();
else
key_wrap_oid = oid;
}
}
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