Implement PBKDF2-based key derivation, random key generation,...

base/crypto/symmetric_key_win.cc

 // Copyright (c) 2010 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 "base/crypto/symmetric_key.h"
 
+#include <winsock2.h>  // For htonl.
+
+#include <vector>
+
+// TODO(wtc): replace scoped_array by std::vector.
+#include "base/scoped_ptr.h"
+
 namespace base {
 
-// TODO(albertb): Implement on Windows.
+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,
+                  DWORD key_size, ScopedHCRYPTKEY* key) {
+  DCHECK_GT(key_size, 0);
+
+  DWORD actual_size = 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 = 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, NULL,
+                           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 = 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()), salt.size(),
+                     0);
+  if (!ok)
+    return false;
+
+  // Iteration U_1: and append (big-endian) INT (i).
+  uint32 big_endian_block_index = htonl(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) {
-  return NULL;
+  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) {
-  return NULL;
+  // 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), &param_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 void* key_data,
+                                   size_t key_size_in_bytes) {
+  // TODO(wtc): support HMAC.
+  DCHECK_EQ(algorithm, AES);
+
+  ScopedHCRYPTPROV provider;
+  BOOL ok = CryptAcquireContext(provider.receive(), NULL, NULL,
+                                PROV_RSA_AES, CRYPT_VERIFYCONTEXT);
+  if (!ok)
+    return NULL;
+
+  ALG_ID alg = GetAESAlgIDForKeySize(key_size_in_bytes * 8);
+  if (alg == 0)
+    return NULL;
+
+  ScopedHCRYPTKEY key;
+  if (!ImportRawKey(provider, alg, key_data, key_size_in_bytes, &key))
+    return NULL;
+
+  return new SymmetricKey(provider.release(), key.release(),
+                          key_data, key_size_in_bytes);
 }
 
 bool SymmetricKey::GetRawKey(std::string* raw_key) {
-  return false;
+  // 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_, NULL, PLAINTEXTKEYBLOB, 0, NULL, &size);
+  if (!ok)
+    return false;
+
+  std::vector<BYTE> result(size);
+
+  ok = CryptExportKey(key_, NULL, 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 base