crypto/openpgp_symmetric

/* [<][>][^][v][top][bottom][index][help] */
This source file includes following definitions.
U8
U32
Prefix
Remainder
tell
Seek
Skip
empty
SaltedIteratedS2K
CreateAESContext
Decrypt
ParsePacket
ParseStreamContents
ParseLength
ParseSymmetricKeyEncrypted
CFBDecrypt
OpenPGPCipherIdToKeyLength
ParseSymmetricallyEncrypted
ParseLiteralData
Encrypt
MakePacket
SerializeLiteralData
SerializeSymmetricKeyEncrypted
SerializeSymmetricallyEncrypted
Decrypt
Encrypt
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "crypto/openpgp_symmetric_encryption.h"

#include <stdlib.h>

#include <sechash.h>
#include <cryptohi.h>

#include <vector>

#include "base/logging.h"
#include "crypto/random.h"
#include "crypto/scoped_nss_types.h"
#include "crypto/nss_util.h"

namespace crypto {

namespace {

// Reader wraps a StringPiece and provides methods to read several datatypes
// while advancing the StringPiece.
class Reader {
 public:
  Reader(base::StringPiece input)
      : data_(input) {
  }

  bool U8(uint8* out) {
    if (data_.size() < 1)
      return false;
    *out = static_cast<uint8>(data_[0]);
    data_.remove_prefix(1);
    return true;
  }

  bool U32(uint32* out) {
    if (data_.size() < 4)
      return false;
    *out = static_cast<uint32>(data_[0]) << 24 |
           static_cast<uint32>(data_[1]) << 16 |
           static_cast<uint32>(data_[2]) << 8 |
           static_cast<uint32>(data_[3]);
    data_.remove_prefix(4);
    return true;
  }

  // Prefix sets |*out| to the first |n| bytes of the StringPiece and advances
  // the StringPiece by |n|.
  bool Prefix(size_t n, base::StringPiece *out) {
    if (data_.size() < n)
      return false;
    *out = base::StringPiece(data_.data(), n);
    data_.remove_prefix(n);
    return true;
  }

  // Remainder returns the remainer of the StringPiece and advances it to the
  // end.
  base::StringPiece Remainder() {
    base::StringPiece ret = data_;
    data_ = base::StringPiece();
    return ret;
  }

  typedef base::StringPiece Position;

  Position tell() const {
    return data_;
  }

  void Seek(Position p) {
    data_ = p;
  }

  bool Skip(size_t n) {
    if (data_.size() < n)
      return false;
    data_.remove_prefix(n);
    return true;
  }

  bool empty() const {
    return data_.empty();
  }

  size_t size() const {
    return data_.size();
  }

 private:
  base::StringPiece data_;
};

// SaltedIteratedS2K implements the salted and iterated string-to-key
// convertion. See RFC 4880, section 3.7.1.3.
void SaltedIteratedS2K(unsigned cipher_key_length,
                       HASH_HashType hash_function,
                       base::StringPiece passphrase,
                       base::StringPiece salt,
                       unsigned count,
                       uint8 *out_key) {
  const std::string combined = salt.as_string() + passphrase.as_string();
  const size_t combined_len = combined.size();

  unsigned done = 0;
  uint8 zero[1] = {0};

  HASHContext* hash_context = HASH_Create(hash_function);

  for (unsigned i = 0; done < cipher_key_length; i++) {
    HASH_Begin(hash_context);

    for (unsigned j = 0; j < i; j++)
      HASH_Update(hash_context, zero, sizeof(zero));

    unsigned written = 0;
    while (written < count) {
      if (written + combined_len > count) {
        unsigned todo = count - written;
        HASH_Update(hash_context,
                     reinterpret_cast<const uint8*>(combined.data()),
                     todo);
        written = count;
      } else {
        HASH_Update(hash_context,
                     reinterpret_cast<const uint8*>(combined.data()),
                     combined_len);
        written += combined_len;
      }
    }

    unsigned num_hash_bytes;
    uint8 digest[HASH_LENGTH_MAX];
    HASH_End(hash_context, digest, &num_hash_bytes, sizeof(digest));

    unsigned todo = cipher_key_length - done;
    if (todo > num_hash_bytes)
      todo = num_hash_bytes;
    memcpy(out_key + done, digest, todo);
    done += todo;
  }

  HASH_Destroy(hash_context);
}

// CreateAESContext sets up |out_key| to be an AES context, with the given key,
// in ECB mode and with no IV.
bool CreateAESContext(const uint8* key, unsigned key_len,
                      ScopedPK11Context* out_decryption_context) {
  ScopedPK11Slot slot(PK11_GetInternalSlot());
  if (!slot.get())
    return false;
  SECItem key_item;
  key_item.type = siBuffer;
  key_item.data = const_cast<uint8*>(key);
  key_item.len = key_len;
  ScopedPK11SymKey pk11_key(PK11_ImportSymKey(
      slot.get(), CKM_AES_ECB, PK11_OriginUnwrap, CKA_ENCRYPT, &key_item,
      NULL));
  if (!pk11_key.get())
    return false;
  ScopedSECItem iv_param(PK11_ParamFromIV(CKM_AES_ECB, NULL));
  out_decryption_context->reset(
      PK11_CreateContextBySymKey(CKM_AES_ECB, CKA_ENCRYPT, pk11_key.get(),
                                 iv_param.get()));
  return out_decryption_context->get() != NULL;
}


// These constants are the tag numbers for the various packet types that we
// use.
static const unsigned kSymmetricKeyEncryptedTag = 3;
static const unsigned kSymmetricallyEncryptedTag = 18;
static const unsigned kCompressedTag = 8;
static const unsigned kLiteralDataTag = 11;

class Decrypter {
 public:
  ~Decrypter() {
    for (std::vector<void*>::iterator
         i = arena_.begin(); i != arena_.end(); i++) {
      free(*i);
    }
    arena_.clear();
  }

  OpenPGPSymmetricEncrytion::Result Decrypt(base::StringPiece in,
                                            base::StringPiece passphrase,
                                            base::StringPiece *out_contents) {
    Reader reader(in);
    unsigned tag;
    base::StringPiece contents;
    ScopedPK11Context decryption_context;

    if (!ParsePacket(&reader, &tag, &contents))
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    if (tag != kSymmetricKeyEncryptedTag)
      return OpenPGPSymmetricEncrytion::NOT_SYMMETRICALLY_ENCRYPTED;
    Reader inner(contents);
    OpenPGPSymmetricEncrytion::Result result =
      ParseSymmetricKeyEncrypted(&inner, passphrase, &decryption_context);
    if (result != OpenPGPSymmetricEncrytion::OK)
      return result;

    if (!ParsePacket(&reader, &tag, &contents))
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    if (tag != kSymmetricallyEncryptedTag)
      return OpenPGPSymmetricEncrytion::NOT_SYMMETRICALLY_ENCRYPTED;
    if (!reader.empty())
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    inner = Reader(contents);
    if (!ParseSymmetricallyEncrypted(&inner, &decryption_context, &contents))
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;

    reader = Reader(contents);
    if (!ParsePacket(&reader, &tag, &contents))
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    if (tag == kCompressedTag)
      return OpenPGPSymmetricEncrytion::COMPRESSED;
    if (tag != kLiteralDataTag)
      return OpenPGPSymmetricEncrytion::NOT_SYMMETRICALLY_ENCRYPTED;
    inner = Reader(contents);
    if (!ParseLiteralData(&inner, out_contents))
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;

    return OpenPGPSymmetricEncrytion::OK;
  }

 private:
  // ParsePacket parses an OpenPGP packet from reader. See RFC 4880, section
  // 4.2.2.
  bool ParsePacket(Reader *reader,
                   unsigned *out_tag,
                   base::StringPiece *out_contents) {
    uint8 header;
    if (!reader->U8(&header))
      return false;
    if ((header & 0x80) == 0) {
      // Tag byte must have MSB set.
      return false;
    }

    if ((header & 0x40) == 0) {
      // Old format packet.
      *out_tag = (header & 0x3f) >> 2;

      uint8 length_type = header & 3;
      if (length_type == 3) {
        *out_contents = reader->Remainder();
        return true;
      }

      const unsigned length_bytes = 1 << length_type;
      size_t length = 0;
      for (unsigned i = 0; i < length_bytes; i++) {
        uint8 length_byte;
        if (!reader->U8(&length_byte))
          return false;
        length <<= 8;
        length |= length_byte;
      }

      return reader->Prefix(length, out_contents);
    }

    // New format packet.
    *out_tag = header & 0x3f;
    size_t length;
    bool is_partial;
    if (!ParseLength(reader, &length, &is_partial))
      return false;
    if (is_partial)
      return ParseStreamContents(reader, length, out_contents);
    return reader->Prefix(length, out_contents);
  }

  // ParseStreamContents parses all the chunks of a partial length stream from
  // reader. See http://tools.ietf.org/html/rfc4880#section-4.2.2.4
  bool ParseStreamContents(Reader *reader,
                           size_t length,
                           base::StringPiece *out_contents) {
    const Reader::Position beginning_of_stream = reader->tell();
    const size_t first_chunk_length = length;

    // First we parse the stream to find its length.
    if (!reader->Skip(length))
      return false;

    for (;;) {
      size_t chunk_length;
      bool is_partial;

      if (!ParseLength(reader, &chunk_length, &is_partial))
        return false;
      if (length + chunk_length < length)
        return false;
      length += chunk_length;
      if (!reader->Skip(chunk_length))
        return false;
      if (!is_partial)
        break;
    }

    // Now we have the length of the whole stream in |length|.
    char* buf = reinterpret_cast<char*>(malloc(length));
    arena_.push_back(buf);
    size_t j = 0;
    reader->Seek(beginning_of_stream);

    base::StringPiece first_chunk;
    if (!reader->Prefix(first_chunk_length, &first_chunk))
      return false;
    memcpy(buf + j, first_chunk.data(), first_chunk_length);
    j += first_chunk_length;

    // Now we parse the stream again, this time copying into |buf|
    for (;;) {
      size_t chunk_length;
      bool is_partial;

      if (!ParseLength(reader, &chunk_length, &is_partial))
        return false;
      base::StringPiece chunk;
      if (!reader->Prefix(chunk_length, &chunk))
        return false;
      memcpy(buf + j, chunk.data(), chunk_length);
      j += chunk_length;
      if (!is_partial)
        break;
    }

    *out_contents = base::StringPiece(buf, length);
    return true;
  }

  // ParseLength parses an OpenPGP length from reader. See RFC 4880, section
  // 4.2.2.
  bool ParseLength(Reader *reader, size_t *out_length, bool *out_is_prefix) {
    uint8 length_spec;
    if (!reader->U8(&length_spec))
      return false;

    *out_is_prefix = false;
    if (length_spec < 192) {
      *out_length = length_spec;
      return true;
    } else if (length_spec < 224) {
      uint8 next_byte;
      if (!reader->U8(&next_byte))
        return false;

      *out_length = (length_spec - 192) << 8;
      *out_length += next_byte;
      return true;
    } else if (length_spec < 255) {
      *out_length = 1u << (length_spec & 0x1f);
      *out_is_prefix = true;
      return true;
    } else {
      uint32 length32;
      if (!reader->U32(&length32))
        return false;
      *out_length = length32;
      return true;
    }
  }

  // ParseSymmetricKeyEncrypted parses a passphrase protected session key. See
  // RFC 4880, section 5.3.
  OpenPGPSymmetricEncrytion::Result ParseSymmetricKeyEncrypted(
      Reader *reader,
      base::StringPiece passphrase,
      ScopedPK11Context *decryption_context) {
    uint8 version, cipher, s2k_type, hash_func_id;
    if (!reader->U8(&version) || version != 4)
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;

    if (!reader->U8(&cipher) ||
        !reader->U8(&s2k_type) ||
        !reader->U8(&hash_func_id)) {
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    }

    uint8 cipher_key_length = OpenPGPCipherIdToKeyLength(cipher);
    if (cipher_key_length == 0)
      return OpenPGPSymmetricEncrytion::UNKNOWN_CIPHER;

    HASH_HashType hash_function;
    switch (hash_func_id) {
    case 2:  // SHA-1
      hash_function = HASH_AlgSHA1;
      break;
    case 8:  // SHA-256
      hash_function = HASH_AlgSHA256;
      break;
    default:
      return OpenPGPSymmetricEncrytion::UNKNOWN_HASH;
    }

    // This chunk of code parses the S2K specifier. See RFC 4880, section 3.7.1.
    base::StringPiece salt;
    uint8 key[32];
    uint8 count_spec;
    switch (s2k_type) {
    case 1:
      if (!reader->Prefix(8, &salt))
        return OpenPGPSymmetricEncrytion::PARSE_ERROR;
      // Fall through.
    case 0:
      SaltedIteratedS2K(cipher_key_length, hash_function, passphrase, salt,
                        passphrase.size() + salt.size(), key);
      break;
    case 3:
      if (!reader->Prefix(8, &salt) ||
          !reader->U8(&count_spec)) {
        return OpenPGPSymmetricEncrytion::PARSE_ERROR;
      }
      SaltedIteratedS2K(
          cipher_key_length, hash_function, passphrase, salt,
          static_cast<unsigned>(
            16 + (count_spec&15)) << ((count_spec >> 4) + 6), key);
      break;
    default:
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    }

    if (!CreateAESContext(key, cipher_key_length, decryption_context))
      return OpenPGPSymmetricEncrytion::INTERNAL_ERROR;

    if (reader->empty()) {
      // The resulting key is used directly.
      return OpenPGPSymmetricEncrytion::OK;
    }

    // The S2K derived key encrypts another key that follows:
    base::StringPiece encrypted_key = reader->Remainder();
    if (encrypted_key.size() < 1)
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;

    uint8* plaintext_key = reinterpret_cast<uint8*>(
        malloc(encrypted_key.size()));
    arena_.push_back(plaintext_key);

    CFBDecrypt(encrypted_key, decryption_context, plaintext_key);

    cipher_key_length = OpenPGPCipherIdToKeyLength(plaintext_key[0]);
    if (cipher_key_length == 0)
      return OpenPGPSymmetricEncrytion::UNKNOWN_CIPHER;
    if (encrypted_key.size() != 1u + cipher_key_length)
      return OpenPGPSymmetricEncrytion::PARSE_ERROR;
    if (!CreateAESContext(plaintext_key + 1, cipher_key_length,
                          decryption_context)) {
      return OpenPGPSymmetricEncrytion::INTERNAL_ERROR;
    }
    return OpenPGPSymmetricEncrytion::OK;
  }

  // CFBDecrypt decrypts the cipher-feedback encrypted data in |in| to |out|
  // using |decryption_context| and assumes an IV of all zeros.
  void CFBDecrypt(base::StringPiece in, ScopedPK11Context* decryption_context,
                  uint8* out) {
    // We need this for PK11_CipherOp to write to, but we never check it as we
    // work in ECB mode, one block at a time.
    int out_len;

    uint8 mask[AES_BLOCK_SIZE];
    memset(mask, 0, sizeof(mask));

    unsigned used = AES_BLOCK_SIZE;

    for (size_t i = 0; i < in.size(); i++) {
      if (used == AES_BLOCK_SIZE) {
        PK11_CipherOp(decryption_context->get(), mask, &out_len, sizeof(mask),
                      mask, AES_BLOCK_SIZE);
        used = 0;
      }

      uint8 t = in[i];
      out[i] = t ^ mask[used];
      mask[used] = t;
      used++;
    }
  }

  // OpenPGPCipherIdToKeyLength converts an OpenPGP cipher id (see RFC 4880,
  // section 9.2) to the key length of that cipher. It returns 0 on error.
  unsigned OpenPGPCipherIdToKeyLength(uint8 cipher) {
    switch (cipher) {
    case 7:  // AES-128
      return 16;
    case 8:  // AES-192
      return 24;
    case 9:  // AES-256
      return 32;
    default:
      return 0;
    }
  }

  // ParseSymmetricallyEncrypted parses a Symmetrically Encrypted packet. See
  // RFC 4880, sections 5.7 and 5.13.
  bool ParseSymmetricallyEncrypted(Reader *reader,
                                   ScopedPK11Context *decryption_context,
                                   base::StringPiece *out_plaintext) {
    // We need this for PK11_CipherOp to write to, but we never check it as we
    // work in ECB mode, one block at a time.
    int out_len;

    uint8 version;
    if (!reader->U8(&version) || version != 1)
      return false;

    base::StringPiece prefix_sp;
    if (!reader->Prefix(AES_BLOCK_SIZE + 2, &prefix_sp))
      return false;
    uint8 prefix[AES_BLOCK_SIZE + 2];
    memcpy(prefix, prefix_sp.data(), sizeof(prefix));

    uint8 prefix_copy[AES_BLOCK_SIZE + 2];
    uint8 fre[AES_BLOCK_SIZE];

    memset(prefix_copy, 0, AES_BLOCK_SIZE);
    PK11_CipherOp(decryption_context->get(), fre, &out_len, sizeof(fre),
                  prefix_copy, AES_BLOCK_SIZE);
    for (unsigned i = 0; i < AES_BLOCK_SIZE; i++)
      prefix_copy[i] = fre[i] ^ prefix[i];
    PK11_CipherOp(decryption_context->get(), fre, &out_len, sizeof(fre), prefix,
                  AES_BLOCK_SIZE);
    prefix_copy[AES_BLOCK_SIZE] = prefix[AES_BLOCK_SIZE] ^ fre[0];
    prefix_copy[AES_BLOCK_SIZE + 1] = prefix[AES_BLOCK_SIZE + 1] ^ fre[1];

    if (prefix_copy[AES_BLOCK_SIZE - 2] != prefix_copy[AES_BLOCK_SIZE] ||
        prefix_copy[AES_BLOCK_SIZE - 1] != prefix_copy[AES_BLOCK_SIZE + 1]) {
      return false;
    }

    fre[0] = prefix[AES_BLOCK_SIZE];
    fre[1] = prefix[AES_BLOCK_SIZE + 1];

    unsigned out_used = 2;

    const size_t plaintext_size = reader->size();
    if (plaintext_size < SHA1_LENGTH + 2) {
      // Too small to contain an MDC trailer.
      return false;
    }

    uint8* plaintext = reinterpret_cast<uint8*>(malloc(plaintext_size));
    arena_.push_back(plaintext);

    for (size_t i = 0; i < plaintext_size; i++) {
      uint8 b;
      if (!reader->U8(&b))
        return false;
      if (out_used == AES_BLOCK_SIZE) {
        PK11_CipherOp(decryption_context->get(), fre, &out_len, sizeof(fre),
                      fre, AES_BLOCK_SIZE);
        out_used = 0;
      }

      plaintext[i] = b ^ fre[out_used];
      fre[out_used++] = b;
    }

    // The plaintext should be followed by a Modification Detection Code
    // packet. This packet is specified such that the header is always
    // serialized as exactly these two bytes:
    if (plaintext[plaintext_size - SHA1_LENGTH - 2] != 0xd3 ||
        plaintext[plaintext_size - SHA1_LENGTH - 1] != 0x14) {
      return false;
    }

    HASHContext* hash_context = HASH_Create(HASH_AlgSHA1);
    HASH_Begin(hash_context);
    HASH_Update(hash_context, prefix_copy, sizeof(prefix_copy));
    HASH_Update(hash_context, plaintext, plaintext_size - SHA1_LENGTH);
    uint8 digest[SHA1_LENGTH];
    unsigned num_hash_bytes;
    HASH_End(hash_context, digest, &num_hash_bytes, sizeof(digest));
    HASH_Destroy(hash_context);

    if (memcmp(digest, &plaintext[plaintext_size - SHA1_LENGTH],
               SHA1_LENGTH) != 0) {
      return false;
    }

    *out_plaintext = base::StringPiece(reinterpret_cast<char*>(plaintext),
                                       plaintext_size - SHA1_LENGTH);
    return true;
  }

  // ParseLiteralData parses a Literal Data packet. See RFC 4880, section 5.9.
  bool ParseLiteralData(Reader *reader, base::StringPiece *out_data) {
    uint8 is_binary, filename_len;
    if (!reader->U8(&is_binary) ||
        !reader->U8(&filename_len) ||
        !reader->Skip(filename_len) ||
        !reader->Skip(sizeof(uint32) /* mtime */)) {
      return false;
    }

    *out_data = reader->Remainder();
    return true;
  }

  // arena_ contains malloced pointers that are used as temporary space during
  // the decryption.
  std::vector<void*> arena_;
};

class Encrypter {
 public:
  // ByteString is used throughout in order to avoid signedness issues with a
  // std::string.
  typedef std::basic_string<uint8> ByteString;

  static ByteString Encrypt(base::StringPiece plaintext,
                            base::StringPiece passphrase) {
    ByteString key;
    ByteString ske = SerializeSymmetricKeyEncrypted(passphrase, &key);

    ByteString literal_data = SerializeLiteralData(plaintext);
    ByteString se = SerializeSymmetricallyEncrypted(literal_data, key);
    return ske + se;
  }

 private:
  // MakePacket returns an OpenPGP packet tagged as type |tag|. It always uses
  // new-format headers. See RFC 4880, section 4.2.
  static ByteString MakePacket(unsigned tag, const ByteString& contents) {
    ByteString header;
    header.push_back(0x80 | 0x40 | tag);

    if (contents.size() < 192) {
      header.push_back(contents.size());
    } else if (contents.size() < 8384) {
      size_t length = contents.size();
      length -= 192;
      header.push_back(192 + (length >> 8));
      header.push_back(length & 0xff);
    } else {
      size_t length = contents.size();
      header.push_back(255);
      header.push_back(length >> 24);
      header.push_back(length >> 16);
      header.push_back(length >> 8);
      header.push_back(length);
    }

    return header + contents;
  }

  // SerializeLiteralData returns a Literal Data packet containing |contents|
  // as binary data with no filename nor mtime specified. See RFC 4880, section
  // 5.9.
  static ByteString SerializeLiteralData(base::StringPiece contents) {
    ByteString literal_data;
    literal_data.push_back(0x74);  // text mode
    literal_data.push_back(0x00);  // no filename
    literal_data.push_back(0x00);  // zero mtime
    literal_data.push_back(0x00);
    literal_data.push_back(0x00);
    literal_data.push_back(0x00);
    literal_data += ByteString(reinterpret_cast<const uint8*>(contents.data()),
                               contents.size());
    return MakePacket(kLiteralDataTag, literal_data);
  }

  // SerializeSymmetricKeyEncrypted generates a random AES-128 key from
  // |passphrase|, sets |out_key| to it and returns a Symmetric Key Encrypted
  // packet. See RFC 4880, section 5.3.
  static ByteString SerializeSymmetricKeyEncrypted(base::StringPiece passphrase,
                                                   ByteString *out_key) {
    ByteString ske;
    ske.push_back(4);  // version 4
    ske.push_back(7);  // AES-128
    ske.push_back(3);  // iterated and salted S2K
    ske.push_back(2);  // SHA-1

    uint64 salt64;
    crypto::RandBytes(&salt64, sizeof(salt64));
    ByteString salt(sizeof(salt64), 0);

    // It's a random value, so endianness doesn't matter.
    ske += ByteString(reinterpret_cast<uint8*>(&salt64), sizeof(salt64));
    ske.push_back(96);  // iteration count of 65536

    uint8 key[16];
    SaltedIteratedS2K(
        sizeof(key), HASH_AlgSHA1, passphrase,
        base::StringPiece(reinterpret_cast<char*>(&salt64), sizeof(salt64)),
        65536, key);
    *out_key = ByteString(key, sizeof(key));
    return MakePacket(kSymmetricKeyEncryptedTag, ske);
  }

  // SerializeSymmetricallyEncrypted encrypts |plaintext| with |key| and
  // returns a Symmetrically Encrypted packet containing the ciphertext. See
  // RFC 4880, section 5.7.
  static ByteString SerializeSymmetricallyEncrypted(ByteString plaintext,
                                                    const ByteString& key) {
    // We need this for PK11_CipherOp to write to, but we never check it as we
    // work in ECB mode, one block at a time.
    int out_len;

    ByteString packet;
    packet.push_back(1);  // version 1
    static const unsigned kBlockSize = 16;  // AES block size

    uint8 prefix[kBlockSize + 2], fre[kBlockSize], iv[kBlockSize];
    crypto::RandBytes(iv, kBlockSize);
    memset(fre, 0, sizeof(fre));

    ScopedPK11Context aes_context;
    CHECK(CreateAESContext(key.data(), key.size(), &aes_context));

    PK11_CipherOp(aes_context.get(), fre, &out_len, sizeof(fre), fre,
                  AES_BLOCK_SIZE);
    for (unsigned i = 0; i < 16; i++)
      prefix[i] = iv[i] ^ fre[i];
    PK11_CipherOp(aes_context.get(), fre, &out_len, sizeof(fre), prefix,
                  AES_BLOCK_SIZE);
    prefix[kBlockSize] = iv[kBlockSize - 2] ^ fre[0];
    prefix[kBlockSize + 1] = iv[kBlockSize - 1] ^ fre[1];

    packet += ByteString(prefix, sizeof(prefix));

    ByteString plaintext_copy = plaintext;
    plaintext_copy.push_back(0xd3);  // MDC packet
    plaintext_copy.push_back(20);  // packet length (20 bytes)

    HASHContext* hash_context = HASH_Create(HASH_AlgSHA1);
    HASH_Begin(hash_context);
    HASH_Update(hash_context, iv, sizeof(iv));
    HASH_Update(hash_context, iv + kBlockSize - 2, 2);
    HASH_Update(hash_context, plaintext_copy.data(), plaintext_copy.size());
    uint8 digest[SHA1_LENGTH];
    unsigned num_hash_bytes;
    HASH_End(hash_context, digest, &num_hash_bytes, sizeof(digest));
    HASH_Destroy(hash_context);

    plaintext_copy += ByteString(digest, sizeof(digest));

    fre[0] = prefix[kBlockSize];
    fre[1] = prefix[kBlockSize+1];
    unsigned out_used = 2;

    for (size_t i = 0; i < plaintext_copy.size(); i++) {
      if (out_used == kBlockSize) {
        PK11_CipherOp(aes_context.get(), fre, &out_len, sizeof(fre), fre,
                      AES_BLOCK_SIZE);
        out_used = 0;
      }

      uint8 c = plaintext_copy[i] ^ fre[out_used];
      fre[out_used++] = c;
      packet.push_back(c);
    }

    return MakePacket(kSymmetricallyEncryptedTag, packet);
  }
};

}  // anonymous namespace

// static
OpenPGPSymmetricEncrytion::Result OpenPGPSymmetricEncrytion::Decrypt(
    base::StringPiece encrypted,
    base::StringPiece passphrase,
    std::string *out) {
  EnsureNSSInit();

  Decrypter decrypter;
  base::StringPiece result;
  Result reader = decrypter.Decrypt(encrypted, passphrase, &result);
  if (reader == OK)
    *out = result.as_string();
  return reader;
}

// static
std::string OpenPGPSymmetricEncrytion::Encrypt(
    base::StringPiece plaintext,
    base::StringPiece passphrase) {
  EnsureNSSInit();

  Encrypter::ByteString b =
      Encrypter::Encrypt(plaintext, passphrase);
  return std::string(reinterpret_cast<const char*>(b.data()), b.size());
}

}  // namespace crypto
/* [<][>][^][v][top][bottom][index][help] */
root/crypto/openpgp_symmetric_encryption.cc

DEFINITIONS
