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110 lines
3.8 KiB
C++
110 lines
3.8 KiB
C++
// hkdf.h - written and placed in public domain by Jeffrey Walton.
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//! \file hkdf.h
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//! \brief Classes for HKDF from RFC 5869
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//! \since Crypto++ 5.6.3
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#ifndef CRYPTOPP_HASH_KEY_DERIVATION_FUNCTION_H
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#define CRYPTOPP_HASH_KEY_DERIVATION_FUNCTION_H
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#include "cryptlib.h"
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#include "hrtimer.h"
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#include "secblock.h"
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#include "hmac.h"
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NAMESPACE_BEGIN(CryptoPP)
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//! abstract base class for key derivation function
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class KeyDerivationFunction
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{
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public:
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//! maximum number of bytes which can be produced under a secuirty context
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virtual size_t MaxDerivedKeyLength() const =0;
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virtual bool Usesinfo() const =0;
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//! derive a key from secret
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virtual unsigned int DeriveKey(byte *derived, size_t derivedLen, const byte *secret, size_t secretLen, const byte *salt, size_t saltLen, const byte* info=NULL, size_t infoLen=0) const =0;
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virtual ~KeyDerivationFunction() {}
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};
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//! \brief Extract-and-Expand Key Derivation Function (HKDF)
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//! \tparam T HashTransformation class
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//! \sa <A HREF="http://eprint.iacr.org/2010/264">Cryptographic Extraction and Key Derivation: The HKDF Scheme</A>
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//! and <A HREF="http://tools.ietf.org/html/rfc5869">HMAC-based Extract-and-Expand Key Derivation Function (HKDF)</A>
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//! \since Crypto++ 5.6.3
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template <class T>
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class HKDF : public KeyDerivationFunction
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{
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public:
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CRYPTOPP_CONSTANT(DIGESTSIZE = T::DIGESTSIZE)
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CRYPTOPP_CONSTANT(SALTSIZE = T::DIGESTSIZE)
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static const char* StaticAlgorithmName () {
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static const std::string name(std::string("HKDF(") + std::string(T::StaticAlgorithmName()) + std::string(")"));
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return name.c_str();
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}
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size_t MaxDerivedKeyLength() const {return static_cast<size_t>(T::DIGESTSIZE) * 255;}
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bool Usesinfo() const {return true;}
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unsigned int 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;
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protected:
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// If salt is missing (NULL), then use the NULL vector. Missing is different than EMPTY (0 length). The length
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// of s_NullVector used depends on the Hash function. SHA-256 will use 32 bytes of s_NullVector.
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typedef byte NullVectorType[SALTSIZE];
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static const NullVectorType& GetNullVector() {
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static const NullVectorType s_NullVector = {0};
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return s_NullVector;
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}
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};
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template <class T>
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unsigned int 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
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{
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static const size_t DIGEST_SIZE = static_cast<size_t>(T::DIGESTSIZE);
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const unsigned int req = static_cast<unsigned int>(derivedLen);
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CRYPTOPP_ASSERT(secret && secretLen);
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CRYPTOPP_ASSERT(derived && derivedLen);
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CRYPTOPP_ASSERT(derivedLen <= MaxDerivedKeyLength());
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if (derivedLen > MaxDerivedKeyLength())
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throw InvalidArgument("HKDF: derivedLen must be less than or equal to MaxDerivedKeyLength");
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HMAC<T> hmac;
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FixedSizeSecBlock<byte, DIGEST_SIZE> prk, buffer;
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// Extract
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const byte* key = (salt ? salt : GetNullVector());
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const size_t klen = (salt ? saltLen : DIGEST_SIZE);
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hmac.SetKey(key, klen);
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hmac.CalculateDigest(prk, secret, secretLen);
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// Expand
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hmac.SetKey(prk.data(), prk.size());
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byte block = 0;
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while (derivedLen > 0)
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{
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if (block++) {hmac.Update(buffer, buffer.size());}
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if (info && infoLen) {hmac.Update(info, infoLen);}
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hmac.CalculateDigest(buffer, &block, 1);
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#if CRYPTOPP_MSC_VERSION
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const size_t segmentLen = STDMIN(derivedLen, DIGEST_SIZE);
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memcpy_s(derived, segmentLen, buffer, segmentLen);
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#else
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const size_t segmentLen = STDMIN(derivedLen, DIGEST_SIZE);
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std::memcpy(derived, buffer, segmentLen);
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#endif
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derived += segmentLen;
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derivedLen -= segmentLen;
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}
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return req;
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}
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NAMESPACE_END
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#endif // CRYPTOPP_HASH_KEY_DERIVATION_FUNCTION_H
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