fizz::HkdfImpl< Hash > Class Template Reference

#include <Hkdf.h>

Inheritance diagram for fizz::HkdfImpl< Hash >:

Public Member Functions
std::vector< uint8_t >	extract (folly::ByteRange salt, folly::ByteRange ikm) const override
std::unique_ptr< folly::IOBuf >	expand (folly::ByteRange extractedKey, const folly::IOBuf &info, size_t outputBytes) const override
std::unique_ptr< folly::IOBuf >	hkdf (folly::ByteRange ikm, folly::ByteRange salt, const folly::IOBuf &info, size_t outputBytes) const override
size_t	hashLength () const override
Public Member Functions inherited from fizz::Hkdf
virtual	~Hkdf ()=default

Static Public Attributes
static constexpr size_t	HashLen = Hash::HashLen

Detailed Description

template<typename Hash>
class fizz::HkdfImpl< Hash >

HKDF implementation using a templated HMAC implementation.

The template struct requires the following parameters:

• HashLen: length of the hash digest
• hmac(ByteRange key, const IOBuf& in, MutableByteRange out)

Definition at line 54 of file Hkdf.h.

Member Function Documentation

template<typename Hash >

std::unique_ptr< folly::IOBuf > fizz::HkdfImpl< Hash >::expand ( folly::ByteRange  extractedKey, const folly::IOBuf &  info, size_t  outputBytes  ) const

inlineoverridevirtual

Implements fizz::Hkdf.

Definition at line 25 of file Hkdf-inl.h.

References folly::IOBuf::clone(), folly::IOBuf::create(), folly::gen::move, folly::range(), folly::chrono::round(), folly::Range< Iter >::size(), and UNLIKELY.

                              {
  CHECK_EQ(extractedKey.size(), Hash::HashLen);
  if (UNLIKELY(outputBytes > 255 * Hash::HashLen)) {
    throw std::runtime_error("Output too long");
  }
  // HDKF expansion step.
  size_t numRounds = (outputBytes + Hash::HashLen - 1) / Hash::HashLen;
  auto expanded = folly::IOBuf::create(numRounds * Hash::HashLen);

  auto in = folly::IOBuf::create(0);
  for (size_t round = 1; round <= numRounds; ++round) {
    in->prependChain(info.clone());
    // We're guaranteed that the round num will fit in
    // one byte because of the check at the beginning of
    // the method.
    auto roundNum = folly::IOBuf::create(1);
    roundNum->append(1);
    roundNum->writableData()[0] = round;
    in->prependChain(std::move(roundNum));

    size_t outputStartIdx = (round - 1) * Hash::HashLen;
    Hash::hmac(
        folly::range(extractedKey),
        *in,
        {expanded->writableData() + outputStartIdx, Hash::HashLen});
    expanded->append(Hash::HashLen);

    in = expanded->clone();
    in->trimStart(outputStartIdx);
  }
  expanded->trimEnd(numRounds * Hash::HashLen - outputBytes);
  return expanded;
}

template<typename Hash >

std::vector< uint8_t > fizz::HkdfImpl< Hash >::extract ( folly::ByteRange  salt, folly::ByteRange  ikm  ) const

inlineoverridevirtual

Implements fizz::Hkdf.

Definition at line 12 of file Hkdf-inl.h.

References folly::Range< Iter >::empty(), folly::range(), and folly::IOBuf::wrapBufferAsValue().

                              {
  auto zeros = std::vector<uint8_t>(Hash::HashLen, 0);
  // Extraction step HMAC-HASH(salt, IKM)
  std::vector<uint8_t> extractedKey(Hash::HashLen);
  salt = salt.empty() ? folly::range(zeros) : salt;
  Hash::hmac(
      salt, folly::IOBuf::wrapBufferAsValue(ikm), folly::range(extractedKey));
  return extractedKey;
}

template<typename Hash>

size_t fizz::HkdfImpl< Hash >::hashLength ( ) const

inlineoverridevirtual

Implements fizz::Hkdf.

Definition at line 72 of file Hkdf.h.

                                     {
    return HashLen;
  }

template<typename Hash >

std::unique_ptr< folly::IOBuf > fizz::HkdfImpl< Hash >::hkdf ( folly::ByteRange  ikm, folly::ByteRange  salt, const folly::IOBuf &  info, size_t  outputBytes  ) const

inlineoverridevirtual

Implements fizz::Hkdf.

Definition at line 63 of file Hkdf-inl.h.

References folly::range().

                              {
  return expand(folly::range(extract(salt, ikm)), info, outputBytes);
}

Member Data Documentation

template<typename Hash>

constexpr size_t fizz::HkdfImpl< Hash >::HashLen = Hash::HashLen

static

Definition at line 56 of file Hkdf.h.

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The documentation for this class was generated from the following files:

• proxygen/fizz/fizz/crypto/Hkdf.h
• proxygen/fizz/fizz/crypto/Hkdf-inl.h