| // 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_array<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_array<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_array<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 |