path: root/net/base/keygen_handler_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 "net/base/keygen_handler.h"

#include <windows.h>
#include <wincrypt.h>
#pragma comment(lib, "crypt32.lib")
#include <rpc.h>
#pragma comment(lib, "rpcrt4.lib")

#include <list>
#include <string>
#include <vector>

#include "base/base64.h"
#include "base/basictypes.h"
#include "base/logging.h"
#include "base/string_piece.h"
#include "base/utf_string_conversions.h"

namespace net {

// TODO(rsleevi): The following encoding functions are adapted from
// base/crypto/rsa_private_key.h and can/should probably be refactored.
static const uint8 kSequenceTag = 0x30;

void PrependLength(size_t size, std::list<BYTE>* data) {
  // The high bit is used to indicate whether additional octets are needed to
  // represent the length.
  if (size < 0x80) {
    data->push_front(static_cast<BYTE>(size));
  } else {
    uint8 num_bytes = 0;
    while (size > 0) {
      data->push_front(static_cast<BYTE>(size & 0xFF));
      size >>= 8;
      num_bytes++;
    }
    CHECK_LE(num_bytes, 4);
    data->push_front(0x80 | num_bytes);
  }
}

void PrependTypeHeaderAndLength(uint8 type, uint32 length,
                                std::vector<BYTE>* output) {
  std::list<BYTE> type_and_length;

  PrependLength(length, &type_and_length);
  type_and_length.push_front(type);

  output->insert(output->begin(), type_and_length.begin(),
                 type_and_length.end());
}

bool EncodeAndAppendType(LPCSTR type, const void* to_encode,
                         std::vector<BYTE>* output) {
  BOOL ok;
  DWORD size = 0;
  ok = CryptEncodeObject(X509_ASN_ENCODING, type, to_encode, NULL, &size);
  DCHECK(ok);
  if (!ok)
    return false;

  std::vector<BYTE>::size_type old_size = output->size();
  output->resize(old_size + size);

  ok = CryptEncodeObject(X509_ASN_ENCODING, type, to_encode,
                         &(*output)[old_size], &size);
  DCHECK(ok);
  if (!ok)
    return false;

  // Sometimes the initial call to CryptEncodeObject gave a generous estimate
  // of the size, so shrink back to what was actually used.
  output->resize(old_size + size);

  return true;
}

// Appends a DER IA5String containing |challenge| to |output|.
// Returns true if encoding was successful.
bool EncodeChallenge(const std::string& challenge, std::vector<BYTE>* output) {
  CERT_NAME_VALUE challenge_nv;
  challenge_nv.dwValueType = CERT_RDN_IA5_STRING;
  challenge_nv.Value.pbData = const_cast<BYTE*>(
      reinterpret_cast<const BYTE*>(challenge.data()));
  challenge_nv.Value.cbData = challenge.size();

  return EncodeAndAppendType(X509_ANY_STRING, &challenge_nv, output);
}

// Appends a DER SubjectPublicKeyInfo structure for the signing key in |prov|
// to |output|.
// Returns true if encoding was successful.
bool EncodeSubjectPublicKeyInfo(HCRYPTPROV prov, std::vector<BYTE>* output) {
  BOOL ok;
  DWORD size = 0;

  // From the private key stored in HCRYPTPROV, obtain the public key, stored
  // as a CERT_PUBLIC_KEY_INFO structure. Currently, only RSA public keys are
  // supported.
  ok = CryptExportPublicKeyInfoEx(prov, AT_KEYEXCHANGE, X509_ASN_ENCODING,
                                  szOID_RSA_RSA, 0, NULL, NULL, &size);
  DCHECK(ok);
  if (!ok)
    return false;

  std::vector<BYTE> public_key_info(size);
  PCERT_PUBLIC_KEY_INFO public_key_casted =
      reinterpret_cast<PCERT_PUBLIC_KEY_INFO>(&public_key_info[0]);
  ok = CryptExportPublicKeyInfoEx(prov, AT_KEYEXCHANGE, X509_ASN_ENCODING,
                                  szOID_RSA_RSA, 0, NULL, public_key_casted,
                                  &size);
  DCHECK(ok);
  if (!ok)
    return false;

  public_key_info.resize(size);

  return EncodeAndAppendType(X509_PUBLIC_KEY_INFO, &public_key_info[0],
                             output);
}

// Generates an ASN.1 DER representation of the PublicKeyAndChallenge structure
// from the signing key of |prov| and the specified |challenge| and appends it
// to |output|.
// True if the the encoding was successfully generated.
bool GetPublicKeyAndChallenge(HCRYPTPROV prov, const std::string& challenge,
                              std::vector<BYTE>* output) {
  if (!EncodeSubjectPublicKeyInfo(prov, output) ||
      !EncodeChallenge(challenge, output)) {
    return false;
  }

  PrependTypeHeaderAndLength(kSequenceTag, output->size(), output);
  return true;
}

// Generates a DER encoded SignedPublicKeyAndChallenge structure from the
// signing key of |prov| and the specified |challenge| string and appends it
// to |output|.
// True if the encoding was successfully generated.
bool GetSignedPublicKeyAndChallenge(HCRYPTPROV prov,
                                    const std::string& challenge,
                                    std::string* output) {
  std::vector<BYTE> pkac;
  if (!GetPublicKeyAndChallenge(prov, challenge, &pkac))
    return false;

  std::vector<BYTE> signature;
  std::vector<BYTE> signed_pkac;
  DWORD size = 0;
  BOOL ok;

  // While the MSDN documentation states that CERT_SIGNED_CONTENT_INFO should
  // be an X.509 certificate type, for encoding this is not necessary. The
  // result of encoding this structure will be a DER-encoded structure with
  // the ASN.1 equivalent of
  //  ::= SEQUENCE {
  //    ToBeSigned IMPLICIT OCTET STRING,
  //    SignatureAlgorithm AlgorithmIdentifier,
  //    Signature BIT STRING
  //  }
  //
  // This happens to be the same naive type as an SPKAC, so this works.
  CERT_SIGNED_CONTENT_INFO info;
  info.ToBeSigned.cbData = pkac.size();
  info.ToBeSigned.pbData = &pkac[0];
  info.SignatureAlgorithm.pszObjId = szOID_RSA_MD5RSA;
  info.SignatureAlgorithm.Parameters.cbData = 0;
  info.SignatureAlgorithm.Parameters.pbData = NULL;

  ok = CryptSignCertificate(prov, AT_KEYEXCHANGE, X509_ASN_ENCODING,
                            info.ToBeSigned.pbData, info.ToBeSigned.cbData,
                            &info.SignatureAlgorithm, NULL, NULL, &size);
  DCHECK(ok);
  if (!ok)
    return false;

  signature.resize(size);
  info.Signature.cbData = signature.size();
  info.Signature.pbData = &signature[0];
  info.Signature.cUnusedBits = 0;

  ok = CryptSignCertificate(prov, AT_KEYEXCHANGE, X509_ASN_ENCODING,
                            info.ToBeSigned.pbData, info.ToBeSigned.cbData,
                            &info.SignatureAlgorithm, NULL,
                            info.Signature.pbData, &info.Signature.cbData);
  DCHECK(ok);
  if (!ok || !EncodeAndAppendType(X509_CERT, &info, &signed_pkac))
    return false;

  output->assign(reinterpret_cast<char*>(&signed_pkac[0]),
                 signed_pkac.size());

  return true;
}

// Generates a unique name for the container which will store the key that is
// generated. The traditional Windows approach is to use a GUID here.
std::wstring GetNewKeyContainerId() {
  RPC_STATUS status = RPC_S_OK;
  std::wstring result;

  UUID id = { 0 };
  status = UuidCreateSequential(&id);
  if (status != RPC_S_OK && status != RPC_S_UUID_LOCAL_ONLY)
    return result;

  RPC_WSTR rpc_string = NULL;
  status = UuidToString(&id, &rpc_string);
  if (status != RPC_S_OK)
    return result;

  // RPC_WSTR is unsigned short*.  wchar_t is a built-in type of Visual C++,
  // so the type cast is necessary.
  result.assign(reinterpret_cast<wchar_t*>(rpc_string));
  RpcStringFree(&rpc_string);

  return result;
}

void StoreKeyLocationInCache(HCRYPTPROV prov) {
  BOOL ok;
  DWORD size = 0;

  // Though it is known the container and provider name, as they are supplied
  // during GenKeyAndSignChallenge, explicitly resolving them via
  // CryptGetProvParam ensures that any defaults (such as provider name being
  // NULL) or any CSP modifications to the container name are properly
  // reflected.

  // Find the container name. Though the MSDN documentation states it will
  // return the exact same value as supplied when the provider was aquired, it
  // also notes the return type will be CHAR, /not/ WCHAR.
  ok = CryptGetProvParam(prov, PP_CONTAINER, NULL, &size, 0);
  if (!ok)
    return;

  std::vector<BYTE> buffer(size);
  ok = CryptGetProvParam(prov, PP_CONTAINER, &buffer[0], &size, 0);
  if (!ok)
    return;

  KeygenHandler::KeyLocation key_location;
  UTF8ToWide(reinterpret_cast<char*>(&buffer[0]), size,
             &key_location.container_name);

  // Get the provider name. This will always resolve, even if NULL (indicating
  // the default provider) was supplied to the CryptAcquireContext.
  size = 0;
  ok = CryptGetProvParam(prov, PP_NAME, NULL, &size, 0);
  if (!ok)
    return;

  buffer.resize(size);
  ok = CryptGetProvParam(prov, PP_NAME, &buffer[0], &size, 0);
  if (!ok)
    return;

  UTF8ToWide(reinterpret_cast<char*>(&buffer[0]), size,
             &key_location.provider_name);

  std::vector<BYTE> public_key_info;
  if (!EncodeSubjectPublicKeyInfo(prov, &public_key_info))
    return;

  KeygenHandler::Cache* cache = KeygenHandler::Cache::GetInstance();
  cache->Insert(std::string(public_key_info.begin(), public_key_info.end()),
                key_location);
}

bool KeygenHandler::KeyLocation::Equals(
    const KeygenHandler::KeyLocation& location) const {
  return container_name == location.container_name &&
         provider_name == location.provider_name;
}

std::string KeygenHandler::GenKeyAndSignChallenge() {
  std::string result;

  bool is_success = true;
  HCRYPTPROV prov = NULL;
  HCRYPTKEY key = NULL;
  DWORD flags = (key_size_in_bits_ << 16) | CRYPT_EXPORTABLE;
  std::string spkac;

  std::wstring new_key_id;

  // TODO(rsleevi): Have the user choose which provider they should use, which
  // needs to be filtered by those providers which can provide the key type
  // requested or the key size requested. This is especially important for
  // generating certificates that will be stored on smart cards.
  const int kMaxAttempts = 5;
  BOOL ok = FALSE;
  for (int attempt = 0; attempt < kMaxAttempts; ++attempt) {
    // Per MSDN documentation for CryptAcquireContext, if applications will be
    // creating their own keys, they should ensure unique naming schemes to
    // prevent overlap with any other applications or consumers of CSPs, and
    // *should not* store new keys within the default, NULL key container.
    new_key_id = GetNewKeyContainerId();
    if (new_key_id.empty())
      return result;

    // Only create new key containers, so that existing key containers are not
    // overwritten.
    ok = CryptAcquireContext(&prov, new_key_id.c_str(), NULL, PROV_RSA_FULL,
                             CRYPT_SILENT | CRYPT_NEWKEYSET);

    if (ok || GetLastError() != NTE_BAD_KEYSET)
      break;
  }
  if (!ok) {
    LOG(ERROR) << "Couldn't acquire a CryptoAPI provider context: "
               << GetLastError();
    is_success = false;
    goto failure;
  }

  if (!CryptGenKey(prov, CALG_RSA_KEYX, flags, &key)) {
    LOG(ERROR) << "Couldn't generate an RSA key";
    is_success = false;
    goto failure;
  }

  if (!GetSignedPublicKeyAndChallenge(prov, challenge_, &spkac)) {
    LOG(ERROR) << "Couldn't generate the signed public key and challenge";
    is_success = false;
    goto failure;
  }

  if (!base::Base64Encode(spkac, &result)) {
    LOG(ERROR) << "Couldn't convert signed key into base64";
    is_success = false;
    goto failure;
  }

  StoreKeyLocationInCache(prov);

 failure:
  if (!is_success) {
    LOG(ERROR) << "SSL Keygen failed";
  } else {
    LOG(INFO) << "SSL Key succeeded";
  }
  if (key) {
    // Securely destroys the handle, but leaves the underlying key alone. The
    // key can be obtained again by resolving the key location. If
    // |stores_key_| is false, the underlying key will be destroyed below.
    CryptDestroyKey(key);
  }

  if (prov) {
    CryptReleaseContext(prov, 0);
    prov = NULL;
    if (!stores_key_) {
      // Fully destroys any of the keys that were created and releases prov.
      CryptAcquireContext(&prov, new_key_id.c_str(), NULL, PROV_RSA_FULL,
                          CRYPT_SILENT | CRYPT_DELETEKEYSET);
    }
  }

  return result;
}

}  // namespace net