// 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/symmetric_key.h"
#include <vector>
// TODO(wtc): replace scoped_array by std::vector.
#include "base/memory/scoped_ptr.h"
#include "base/sys_byteorder.h"
namespace crypto {
namespace {
// The following is a non-public Microsoft header documented in MSDN under
// CryptImportKey / CryptExportKey. Following the header is the byte array of
// the actual plaintext key.
struct PlaintextBlobHeader {
BLOBHEADER hdr;
DWORD cbKeySize;
};
// CryptoAPI makes use of three distinct ALG_IDs for AES, rather than just
// CALG_AES (which exists, but depending on the functions you are calling, may
// result in function failure, whereas the subtype would succeed).
ALG_ID GetAESAlgIDForKeySize(size_t key_size_in_bits) {
// Only AES-128/-192/-256 is supported in CryptoAPI.
switch (key_size_in_bits) {
case 128:
return CALG_AES_128;
case 192:
return CALG_AES_192;
case 256:
return CALG_AES_256;
default:
NOTREACHED();
return 0;
}
};
// Imports a raw/plaintext key of |key_size| stored in |*key_data| into a new
// key created for the specified |provider|. |alg| contains the algorithm of
// the key being imported.
// If |key_data| is intended to be used as an HMAC key, then |alg| should be
// CALG_HMAC.
// If successful, returns true and stores the imported key in |*key|.
// TODO(wtc): use this function in hmac_win.cc.
bool ImportRawKey(HCRYPTPROV provider,
ALG_ID alg,
const void* key_data, size_t key_size,
ScopedHCRYPTKEY* key) {
DCHECK_GT(key_size, 0);
DWORD actual_size =
static_cast<DWORD>(sizeof(PlaintextBlobHeader) + key_size);
std::vector<BYTE> tmp_data(actual_size);
BYTE* actual_key = &tmp_data[0];
memcpy(actual_key + sizeof(PlaintextBlobHeader), key_data, key_size);
PlaintextBlobHeader* key_header =
reinterpret_cast<PlaintextBlobHeader*>(actual_key);
memset(key_header, 0, sizeof(PlaintextBlobHeader));
key_header->hdr.bType = PLAINTEXTKEYBLOB;
key_header->hdr.bVersion = CUR_BLOB_VERSION;
key_header->hdr.aiKeyAlg = alg;
key_header->cbKeySize = static_cast<DWORD>(key_size);
HCRYPTKEY unsafe_key = NULL;
DWORD flags = CRYPT_EXPORTABLE;
if (alg == CALG_HMAC) {
// Though it may appear odd that IPSEC and RC2 are being used, this is
// done in accordance with Microsoft's FIPS 140-2 Security Policy for the
// RSA Enhanced Provider, as the approved means of using arbitrary HMAC
// key material.
key_header->hdr.aiKeyAlg = CALG_RC2;
flags |= CRYPT_IPSEC_HMAC_KEY;
}
BOOL ok =
CryptImportKey(provider, actual_key, actual_size, 0, flags, &unsafe_key);
// Clean up the temporary copy of key, regardless of whether it was imported
// sucessfully or not.
SecureZeroMemory(actual_key, actual_size);
if (!ok)
return false;
key->reset(unsafe_key);
return true;
}
// Attempts to generate a random AES key of |key_size_in_bits|. Returns true
// if generation is successful, storing the generated key in |*key| and the
// key provider (CSP) in |*provider|.
bool GenerateAESKey(size_t key_size_in_bits,
ScopedHCRYPTPROV* provider,
ScopedHCRYPTKEY* key) {
DCHECK(provider);
DCHECK(key);
ALG_ID alg = GetAESAlgIDForKeySize(key_size_in_bits);
if (alg == 0)
return false;
ScopedHCRYPTPROV safe_provider;
// Note: The only time NULL is safe to be passed as pszContainer is when
// dwFlags contains CRYPT_VERIFYCONTEXT, as all keys generated and/or used
// will be treated as ephemeral keys and not persisted.
BOOL ok = CryptAcquireContext(safe_provider.receive(), NULL, NULL,
PROV_RSA_AES, CRYPT_VERIFYCONTEXT);
if (!ok)
return false;
ScopedHCRYPTKEY safe_key;
// In the FIPS 140-2 Security Policy for CAPI on XP/Vista+, Microsoft notes
// that CryptGenKey makes use of the same functionality exposed via
// CryptGenRandom. The reason this is being used, as opposed to
// CryptGenRandom and CryptImportKey is for compliance with the security
// policy
ok = CryptGenKey(safe_provider.get(), alg, CRYPT_EXPORTABLE,
safe_key.receive());
if (!ok)
return false;
key->swap(safe_key);
provider->swap(safe_provider);
return true;
}
// Returns true if the HMAC key size meets the requirement of FIPS 198
// Section 3. |alg| is the hash function used in the HMAC.
bool CheckHMACKeySize(size_t key_size_in_bits, ALG_ID alg) {
DWORD hash_size = 0;
switch (alg) {
case CALG_SHA1:
hash_size = 20;
break;
case CALG_SHA_256:
hash_size = 32;
break;
case CALG_SHA_384:
hash_size = 48;
break;
case CALG_SHA_512:
hash_size = 64;
break;
}
if (hash_size == 0)
return false;
// An HMAC key must be >= L/2, where L is the output size of the hash
// function being used.
return (key_size_in_bits >= (hash_size / 2 * 8) &&
(key_size_in_bits % 8) == 0);
}
// Attempts to generate a random, |key_size_in_bits|-long HMAC key, for use
// with the hash function |alg|.
// |key_size_in_bits| must be >= 1/2 the hash size of |alg| for security.
// Returns true if generation is successful, storing the generated key in
// |*key| and the key provider (CSP) in |*provider|.
bool GenerateHMACKey(size_t key_size_in_bits,
ALG_ID alg,
ScopedHCRYPTPROV* provider,
ScopedHCRYPTKEY* key,
scoped_ptr<BYTE[]>* raw_key) {
DCHECK(provider);
DCHECK(key);
DCHECK(raw_key);
if (!CheckHMACKeySize(key_size_in_bits, alg))
return false;
ScopedHCRYPTPROV safe_provider;
// See comment in GenerateAESKey as to why NULL is acceptable for the
// container name.
BOOL ok = CryptAcquireContext(safe_provider.receive(), NULL, NULL,
PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
if (!ok)
return false;
DWORD key_size_in_bytes = static_cast<DWORD>(key_size_in_bits / 8);
scoped_ptr<BYTE[]> random(new BYTE[key_size_in_bytes]);
ok = CryptGenRandom(safe_provider, key_size_in_bytes, random.get());
if (!ok)
return false;
ScopedHCRYPTKEY safe_key;
bool rv = ImportRawKey(safe_provider, CALG_HMAC, random.get(),
key_size_in_bytes, &safe_key);
if (rv) {
key->swap(safe_key);
provider->swap(safe_provider);
raw_key->swap(random);
}
SecureZeroMemory(random.get(), key_size_in_bytes);
return rv;
}
// Attempts to create an HMAC hash instance using the specified |provider|
// and |key|. The inner hash function will be |hash_alg|. If successful,
// returns true and stores the hash in |*hash|.
// TODO(wtc): use this function in hmac_win.cc.
bool CreateHMACHash(HCRYPTPROV provider,
HCRYPTKEY key,
ALG_ID hash_alg,
ScopedHCRYPTHASH* hash) {
ScopedHCRYPTHASH safe_hash;
BOOL ok = CryptCreateHash(provider, CALG_HMAC, key, 0, safe_hash.receive());
if (!ok)
return false;
HMAC_INFO hmac_info;
memset(&hmac_info, 0, sizeof(hmac_info));
hmac_info.HashAlgid = hash_alg;
ok = CryptSetHashParam(safe_hash, HP_HMAC_INFO,
reinterpret_cast<const BYTE*>(&hmac_info), 0);
if (!ok)
return false;
hash->swap(safe_hash);
return true;
}
// Computes a block of the derived key using the PBKDF2 function F for the
// specified |block_index| using the PRF |hash|, writing the output to
// |output_buf|.
// |output_buf| must have enough space to accomodate the output of the PRF
// specified by |hash|.
// Returns true if the block was successfully computed.
bool ComputePBKDF2Block(HCRYPTHASH hash,
DWORD hash_size,
const std::string& salt,
size_t iterations,
uint32 block_index,
BYTE* output_buf) {
// From RFC 2898:
// 3. <snip> The function F is defined as the exclusive-or sum of the first
// c iterates of the underlying pseudorandom function PRF applied to the
// password P and the concatenation of the salt S and the block index i:
// F (P, S, c, i) = U_1 \xor U_2 \xor ... \xor U_c
// where
// U_1 = PRF(P, S || INT (i))
// U_2 = PRF(P, U_1)
// ...
// U_c = PRF(P, U_{c-1})
ScopedHCRYPTHASH safe_hash;
BOOL ok = CryptDuplicateHash(hash, NULL, 0, safe_hash.receive());
if (!ok)
return false;
// Iteration U_1: Compute PRF for S.
ok = CryptHashData(safe_hash, reinterpret_cast<const BYTE*>(salt.data()),
static_cast<DWORD>(salt.size()), 0);
if (!ok)
return false;
// Iteration U_1: and append (big-endian) INT (i).
uint32 big_endian_block_index = base::HostToNet32(block_index);
ok = CryptHashData(safe_hash,
reinterpret_cast<BYTE*>(&big_endian_block_index),
sizeof(big_endian_block_index), 0);
std::vector<BYTE> hash_value(hash_size);
DWORD size = hash_size;
ok = CryptGetHashParam(safe_hash, HP_HASHVAL, &hash_value[0], &size, 0);
if (!ok || size != hash_size)
return false;
memcpy(output_buf, &hash_value[0], hash_size);
// Iteration 2 - c: Compute U_{iteration} by applying the PRF to
// U_{iteration - 1}, then xor the resultant hash with |output|, which
// contains U_1 ^ U_2 ^ ... ^ U_{iteration - 1}.
for (size_t iteration = 2; iteration <= iterations; ++iteration) {
safe_hash.reset();
ok = CryptDuplicateHash(hash, NULL, 0, safe_hash.receive());
if (!ok)
return false;
ok = CryptHashData(safe_hash, &hash_value[0], hash_size, 0);
if (!ok)
return false;
size = hash_size;
ok = CryptGetHashParam(safe_hash, HP_HASHVAL, &hash_value[0], &size, 0);
if (!ok || size != hash_size)
return false;
for (int i = 0; i < hash_size; ++i)
output_buf[i] ^= hash_value[i];
}
return true;
}
} // namespace
SymmetricKey::~SymmetricKey() {
// TODO(wtc): create a "secure" string type that zeroes itself in the
// destructor.
if (!raw_key_.empty())
SecureZeroMemory(const_cast<char *>(raw_key_.data()), raw_key_.size());
}
// static
SymmetricKey* SymmetricKey::GenerateRandomKey(Algorithm algorithm,
size_t key_size_in_bits) {
DCHECK_GE(key_size_in_bits, 8);
ScopedHCRYPTPROV provider;
ScopedHCRYPTKEY key;
bool ok = false;
scoped_ptr<BYTE[]> raw_key;
switch (algorithm) {
case AES:
ok = GenerateAESKey(key_size_in_bits, &provider, &key);
break;
case HMAC_SHA1:
ok = GenerateHMACKey(key_size_in_bits, CALG_SHA1, &provider,
&key, &raw_key);
break;
}
if (!ok) {
NOTREACHED();
return NULL;
}
size_t key_size_in_bytes = key_size_in_bits / 8;
if (raw_key == NULL)
key_size_in_bytes = 0;
SymmetricKey* result = new SymmetricKey(provider.release(),
key.release(),
raw_key.get(),
key_size_in_bytes);
if (raw_key != NULL)
SecureZeroMemory(raw_key.get(), key_size_in_bytes);
return result;
}
// static
SymmetricKey* SymmetricKey::DeriveKeyFromPassword(Algorithm algorithm,
const std::string& password,
const std::string& salt,
size_t iterations,
size_t key_size_in_bits) {
// CryptoAPI lacks routines to perform PBKDF2 derivation as specified
// in RFC 2898, so it must be manually implemented. Only HMAC-SHA1 is
// supported as the PRF.
// While not used until the end, sanity-check the input before proceeding
// with the expensive computation.
DWORD provider_type = 0;
ALG_ID alg = 0;
switch (algorithm) {
case AES:
provider_type = PROV_RSA_AES;
alg = GetAESAlgIDForKeySize(key_size_in_bits);
break;
case HMAC_SHA1:
provider_type = PROV_RSA_FULL;
alg = CALG_HMAC;
break;
default:
NOTREACHED();
break;
}
if (provider_type == 0 || alg == 0)
return NULL;
ScopedHCRYPTPROV provider;
BOOL ok = CryptAcquireContext(provider.receive(), NULL, NULL, provider_type,
CRYPT_VERIFYCONTEXT);
if (!ok)
return NULL;
// Convert the user password into a key suitable to be fed into the PRF
// function.
ScopedHCRYPTKEY password_as_key;
BYTE* password_as_bytes =
const_cast<BYTE*>(reinterpret_cast<const BYTE*>(password.data()));
if (!ImportRawKey(provider, CALG_HMAC, password_as_bytes,
password.size(), &password_as_key))
return NULL;
// Configure the PRF function. Only HMAC variants are supported, with the
// only hash function supported being SHA1.
// TODO(rsleevi): Support SHA-256 on XP SP3+.
ScopedHCRYPTHASH prf;
if (!CreateHMACHash(provider, password_as_key, CALG_SHA1, &prf))
return NULL;
DWORD hLen = 0;
DWORD param_size = sizeof(hLen);
ok = CryptGetHashParam(prf, HP_HASHSIZE,
reinterpret_cast<BYTE*>(&hLen), ¶m_size, 0);
if (!ok || hLen == 0)
return NULL;
// 1. If dkLen > (2^32 - 1) * hLen, output "derived key too long" and stop.
size_t dkLen = key_size_in_bits / 8;
DCHECK_GT(dkLen, 0);
if ((dkLen / hLen) > 0xFFFFFFFF) {
DLOG(ERROR) << "Derived key too long.";
return NULL;
}
// 2. Let l be the number of hLen-octet blocks in the derived key,
// rounding up, and let r be the number of octets in the last
// block:
size_t L = (dkLen + hLen - 1) / hLen;
DCHECK_GT(L, 0);
size_t total_generated_size = L * hLen;
std::vector<BYTE> generated_key(total_generated_size);
BYTE* block_offset = &generated_key[0];
// 3. For each block of the derived key apply the function F defined below
// to the password P, the salt S, the iteration count c, and the block
// index to compute the block:
// T_1 = F (P, S, c, 1)
// T_2 = F (P, S, c, 2)
// ...
// T_l = F (P, S, c, l)
// <snip>
// 4. Concatenate the blocks and extract the first dkLen octets to produce
// a derived key DK:
// DK = T_1 || T_2 || ... || T_l<0..r-1>
for (uint32 block_index = 1; block_index <= L; ++block_index) {
if (!ComputePBKDF2Block(prf, hLen, salt, iterations, block_index,
block_offset))
return NULL;
block_offset += hLen;
}
// Convert the derived key bytes into a key handle for the desired algorithm.
ScopedHCRYPTKEY key;
if (!ImportRawKey(provider, alg, &generated_key[0], dkLen, &key))
return NULL;
SymmetricKey* result = new SymmetricKey(provider.release(), key.release(),
&generated_key[0], dkLen);
SecureZeroMemory(&generated_key[0], total_generated_size);
return result;
}
// static
SymmetricKey* SymmetricKey::Import(Algorithm algorithm,
const std::string& raw_key) {
DWORD provider_type = 0;
ALG_ID alg = 0;
switch (algorithm) {
case AES:
provider_type = PROV_RSA_AES;
alg = GetAESAlgIDForKeySize(raw_key.size() * 8);
break;
case HMAC_SHA1:
provider_type = PROV_RSA_FULL;
alg = CALG_HMAC;
break;
default:
NOTREACHED();
break;
}
if (provider_type == 0 || alg == 0)
return NULL;
ScopedHCRYPTPROV provider;
BOOL ok = CryptAcquireContext(provider.receive(), NULL, NULL, provider_type,
CRYPT_VERIFYCONTEXT);
if (!ok)
return NULL;
ScopedHCRYPTKEY key;
if (!ImportRawKey(provider, alg, raw_key.data(), raw_key.size(), &key))
return NULL;
return new SymmetricKey(provider.release(), key.release(),
raw_key.data(), raw_key.size());
}
bool SymmetricKey::GetRawKey(std::string* raw_key) {
// Short circuit for when the key was supplied to the constructor.
if (!raw_key_.empty()) {
*raw_key = raw_key_;
return true;
}
DWORD size = 0;
BOOL ok = CryptExportKey(key_, 0, PLAINTEXTKEYBLOB, 0, NULL, &size);
if (!ok)
return false;
std::vector<BYTE> result(size);
ok = CryptExportKey(key_, 0, PLAINTEXTKEYBLOB, 0, &result[0], &size);
if (!ok)
return false;
PlaintextBlobHeader* header =
reinterpret_cast<PlaintextBlobHeader*>(&result[0]);
raw_key->assign(reinterpret_cast<char*>(&result[sizeof(*header)]),
header->cbKeySize);
SecureZeroMemory(&result[0], size);
return true;
}
SymmetricKey::SymmetricKey(HCRYPTPROV provider,
HCRYPTKEY key,
const void* key_data, size_t key_size_in_bytes)
: provider_(provider), key_(key) {
if (key_data) {
raw_key_.assign(reinterpret_cast<const char*>(key_data),
key_size_in_bytes);
}
}
} // namespace crypto