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// hkdf.h - written and placed in public domain by Jeffrey Walton.
/// \file hkdf.h
/// \brief Classes for HKDF from RFC 5869
/// \since Crypto++ 5.6.3
#ifndef CRYPTOPP_HKDF_H
#define CRYPTOPP_HKDF_H
#include "cryptlib.h"
#include "secblock.h"
#include "hmac.h"
NAMESPACE_BEGIN(CryptoPP)
/// \brief Extract-and-Expand Key Derivation Function (HKDF)
/// \tparam T HashTransformation class
/// \sa <A HREF="http://eprint.iacr.org/2010/264">Cryptographic Extraction and Key
/// Derivation: The HKDF Scheme</A> and
/// <A HREF="http://tools.ietf.org/html/rfc5869">HMAC-based Extract-and-Expand Key
/// Derivation Function (HKDF)</A>
/// \since Crypto++ 5.6.3
template <class T>
class HKDF : public KeyDerivationFunction
{
public:
virtual ~HKDF() {}
static std::string StaticAlgorithmName () {
const std::string name(std::string("HKDF(") +
std::string(T::StaticAlgorithmName()) + std::string(")"));
return name;
}
// KeyDerivationFunction interface
std::string AlgorithmName() const {
return StaticAlgorithmName();
}
// KeyDerivationFunction interface
size_t MaxDerivedLength() const {
return static_cast<size_t>(T::DIGESTSIZE) * 255;
}
// KeyDerivationFunction interface
size_t GetValidDerivedLength(size_t keylength) const;
// KeyDerivationFunction interface
size_t DeriveKey(byte *derived, size_t derivedLen, const byte *secret, size_t secretLen,
const NameValuePairs& params) const;
/// \brief Derive a key from a seed
/// \param derived the derived output buffer
/// \param derivedLen the size of the derived buffer, in bytes
/// \param secret the seed input buffer
/// \param secretLen the size of the secret buffer, in bytes
/// \param salt the salt input buffer
/// \param saltLen the size of the salt buffer, in bytes
/// \param info the additional input buffer
/// \param infoLen the size of the info buffer, in bytes
/// \returns the number of iterations performed
/// \throws InvalidDerivedLength if <tt>derivedLen</tt> is invalid for the scheme
/// \details DeriveKey() provides a standard interface to derive a key from
/// a seed and other parameters. Each class that derives from KeyDerivationFunction
/// provides an overload that accepts most parameters used by the derivation function.
/// \details <tt>salt</tt> and <tt>info</tt> can be <tt>nullptr</tt> with 0 length.
/// HKDF is unusual in that a non-NULL salt with length 0 is different than a
/// NULL <tt>salt</tt>. A NULL <tt>salt</tt> causes HKDF to use a string of 0's
/// of length <tt>T::DIGESTSIZE</tt> for the <tt>salt</tt>.
/// \details HKDF always returns 1 because it only performs 1 iteration. Other
/// derivation functions, like PBKDF's, will return more interesting values.
size_t DeriveKey(byte *derived, size_t derivedLen, const byte *secret, size_t secretLen,
const byte *salt, size_t saltLen, const byte* info, size_t infoLen) const;
protected:
// KeyDerivationFunction interface
const Algorithm & GetAlgorithm() const {
return *this;
}
// If salt is absent (NULL), then use the NULL vector. Missing is different than
// EMPTY (Non-NULL, 0 length). The length of s_NullVector used depends on the Hash
// function. SHA-256 will use 32 bytes of s_NullVector.
typedef byte NullVectorType[T::DIGESTSIZE];
static const NullVectorType& GetNullVector() {
static const NullVectorType s_NullVector = {0};
return s_NullVector;
}
};
template <class T>
size_t HKDF<T>::GetValidDerivedLength(size_t keylength) const
{
if (keylength > MaxDerivedLength())
return MaxDerivedLength();
return keylength;
}
template <class T>
size_t HKDF<T>::DeriveKey(byte *derived, size_t derivedLen,
const byte *secret, size_t secretLen, const NameValuePairs& params) const
{
CRYPTOPP_ASSERT(secret && secretLen);
CRYPTOPP_ASSERT(derived && derivedLen);
CRYPTOPP_ASSERT(derivedLen <= MaxDerivedLength());
ConstByteArrayParameter p;
SecByteBlock salt, info;
if (params.GetValue("Salt", p))
salt.Assign(p.begin(), p.size());
else
salt.Assign(GetNullVector(), T::DIGESTSIZE);
if (params.GetValue("Info", p))
info.Assign(p.begin(), p.size());
else
info.Assign(GetNullVector(), 0);
return DeriveKey(derived, derivedLen, secret, secretLen, salt.begin(), salt.size(), info.begin(), info.size());
}
template <class T>
size_t HKDF<T>::DeriveKey(byte *derived, size_t derivedLen, const byte *secret, size_t secretLen,
const byte *salt, size_t saltLen, const byte* info, size_t infoLen) const
{
CRYPTOPP_ASSERT(secret && secretLen);
CRYPTOPP_ASSERT(derived && derivedLen);
CRYPTOPP_ASSERT(derivedLen <= MaxDerivedLength());
ThrowIfInvalidDerivedLength(derivedLen);
// HKDF business logic. NULL is different than empty.
if (salt == NULLPTR)
{
salt = GetNullVector();
saltLen = T::DIGESTSIZE;
}
// key is PRK from the RFC, salt is IKM from the RFC
HMAC<T> hmac;
SecByteBlock key(T::DIGESTSIZE), buffer(T::DIGESTSIZE);
// Extract
hmac.SetKey(salt, saltLen);
hmac.CalculateDigest(key, secret, secretLen);
// Key
hmac.SetKey(key.begin(), key.size());
byte block = 0;
// Expand
while (derivedLen > 0)
{
if (block++) {hmac.Update(buffer, buffer.size());}
if (infoLen) {hmac.Update(info, infoLen);}
hmac.CalculateDigest(buffer, &block, 1);
#if CRYPTOPP_MSC_VERSION
const size_t digestSize = static_cast<size_t>(T::DIGESTSIZE);
const size_t segmentLen = STDMIN(derivedLen, digestSize);
memcpy_s(derived, segmentLen, buffer, segmentLen);
#else
const size_t digestSize = static_cast<size_t>(T::DIGESTSIZE);
const size_t segmentLen = STDMIN(derivedLen, digestSize);
std::memcpy(derived, buffer, segmentLen);
#endif
derived += segmentLen;
derivedLen -= segmentLen;
}
return 1;
}
NAMESPACE_END
#endif // CRYPTOPP_HKDF_H
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