Add net/android/keystore.h

net/android/keystore_openssl.cc

+// Copyright (c) 2013 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/android/keystore_openssl.h"
+
+#include <jni.h>
+#include <openssl/bn.h>
+// This include is required to get the ECDSA_METHOD structure definition
+// which isn't currently part of the OpenSSL official ABI. This should
+// not be a concern for Chromium which always links against its own
+// version of the library on Android.
+#include <openssl/crypto/ecdsa/ecs_locl.h>
+// And this one is needed for the EC_GROUP definition.
+#include <openssl/crypto/ec/ec_lcl.h>
+#include <openssl/dsa.h>
+#include <openssl/ec.h>
+#include <openssl/engine.h>
+#include <openssl/evp.h>
+#include <openssl/rsa.h>
+
+#include "base/android/build_info.h"
+#include "base/android/jni_android.h"
+#include "base/android/scoped_java_ref.h"
+#include "base/basictypes.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "crypto/openssl_util.h"
+#include "net/android/keystore.h"
+#include "net/base/ssl_client_cert_type.h"
+
+// IMPORTANT NOTE: The following code will currently only work when used
+// to implement client certificate support with OpenSSL. That's because
+// only the signing operations used in this use case are implemented here.
+//
+// Generally speaking, OpenSSL provides many different ways to sign
+// digests. This code doesn't support all these cases, only the ones that
+// are required to sign the MAC during the OpenSSL handshake for TLS < 1.2.
+//
+// The OpenSSL EVP_PKEY type is a generic wrapper around key pairs.
+// Internally, it can hold a pointer to a RSA, DSA or ECDSA structure,
+// which model keypair implementations of each respective crypto
+// algorithm.
+//
+// The RSA type has a 'method' field pointer to a vtable-like structure
+// called a RSA_METHOD. This contains several function pointers that
+// correspond to operations on RSA keys (e.g. decode/encode with public
+// key, decode/encode with private key, signing, validation), as well as
+// a few flags.
+//
+// For example, the RSA_sign() function will call "method->rsa_sign()" if
+// method->rsa_sign is not NULL, otherwise, it will perform a regular
+// signing operation using the other fields in the RSA structure (which
+// are used to hold the typical modulus / exponent / parameters for the
+// key pair).
+//
+// This source file thus defines a custom RSA_METHOD structure, which
+// fields points to static methods used to implement the corresponding
+// RSA operation using platform Android APIs.
+//
+// However, the platform APIs require a jobject JNI reference to work.
+// It must be stored in the RSA instance, or made accessible when the
+// custom RSA methods are called. This is done by using RSA_set_app_data()
+// and RSA_get_app_data().
+//
+// One can thus _directly_ create a new EVP_PKEY that uses a custom RSA
+// object with the following:
+//
+//    RSA* rsa = RSA_new()
+//    RSA_set_method(&custom_rsa_method);
+//    RSA_set_app_data(rsa, jni_private_key);
+//
+//    EVP_PKEY* pkey = EVP_PKEY_new();
+//    EVP_PKEY_assign_RSA(pkey, rsa);
+//
+// Note that because EVP_PKEY_assign_RSA() is used, instead of
+// EVP_PKEY_set1_RSA(), the new EVP_PKEY now owns the RSA object, and
+// will destroy it when it is itself destroyed.
+//
+// Unfortunately, such objects cannot be used with RSA_size(), which
+// totally ignores the RSA_METHOD pointers. Instead, it is necessary
+// to manually setup the modulus field (n) in the RSA object, with a
+// value that matches the wrapped PrivateKey object. See GetRsaPkeyWrapper
+// for full details.
+//
+// Similarly, custom DSA_METHOD and ECDSA_METHOD are defined by this source
+// file, and appropriate field setups are performed to ensure that
+// DSA_size() and ECDSA_size() work properly with the wrapper EVP_PKEY.
+//
+// Note that there is no need to define an OpenSSL ENGINE here. These
+// are objects that can be used to expose custom methods (i.e. either
+// RSA_METHOD, DSA_METHOD, ECDSA_METHOD, and a large number of other ones
+// for types not related to this source file), and make them used by
+// default for a lot of operations. Very fortunately, this is not needed
+// here, which saves a lot of complexity.
+
+using base::android::ScopedJavaGlobalRef;
+
+namespace net {
+namespace android {
+
+namespace {
+
+typedef crypto::ScopedOpenSSL<EVP_PKEY, EVP_PKEY_free> ScopedEVP_PKEY;
+typedef crypto::ScopedOpenSSL<RSA, RSA_free> ScopedRSA;
+typedef crypto::ScopedOpenSSL<DSA, DSA_free> ScopedDSA;
+typedef crypto::ScopedOpenSSL<EC_KEY, EC_KEY_free> ScopedEC_KEY;
+typedef crypto::ScopedOpenSSL<EC_GROUP, EC_GROUP_free> ScopedEC_GROUP;
+
+// Custom RSA_METHOD that uses the platform APIs.
+// Note that for now, only signing through RSA_sign() is really supported.
+// all other method pointers are either stubs returning errors, or no-ops.
+// See <openssl/rsa.h> for exact declaration of RSA_METHOD.
+
+int RsaMethodPubEnc(int flen,
+                    const unsigned char* from,
+                    unsigned char* to,
+                    RSA* rsa,
+                    int padding) {
+  NOTIMPLEMENTED();
+  RSAerr(RSA_F_RSA_PUBLIC_ENCRYPT, RSA_R_RSA_OPERATIONS_NOT_SUPPORTED);
+  return -1;
+}
+
+int RsaMethodPubDec(int flen,
+                    const unsigned char* from,
+                    unsigned char* to,
+                    RSA* rsa,
+                    int padding) {
+  NOTIMPLEMENTED();
+  RSAerr(RSA_F_RSA_PUBLIC_DECRYPT, RSA_R_RSA_OPERATIONS_NOT_SUPPORTED);
+  return -1;
+}
+
+int RsaMethodPrivEnc(int flen,
+                     const unsigned char *from,
+                     unsigned char *to,
+                     RSA *rsa,
+                     int padding) {
+  NOTIMPLEMENTED();
+  RSAerr(RSA_F_RSA_PRIVATE_ENCRYPT, RSA_R_RSA_OPERATIONS_NOT_SUPPORTED);
+  return -1;
+}
+
+int RsaMethodPrivDec(int flen,
+                     const unsigned char* from,
+                     unsigned char* to,
+                     RSA* rsa,
+                     int padding) {
+  NOTIMPLEMENTED();
+  RSAerr(RSA_F_RSA_PRIVATE_DECRYPT, RSA_R_RSA_OPERATIONS_NOT_SUPPORTED);
+  return -1;
+}
+
+int RsaMethodInit(RSA* rsa) {
+  // Required to ensure that RsaMethodSign will be called.
+  rsa->flags |= RSA_FLAG_SIGN_VER;
+  return 0;
+}
+
+int RsaMethodFinish(RSA* rsa) {
+  // Ensure the global JNI reference is destroyed with this key.
+  jobject key = reinterpret_cast<jobject>(RSA_get_app_data(rsa));
+  if (key != NULL) {
+    RSA_set_app_data(rsa, NULL);
+    JNIEnv* env = base::android::AttachCurrentThread();
+    env->DeleteGlobalRef(key);
+  }
+  // Actual return value is ignored by OpenSSL. There are no docs
+  // explaining what this is supposed to be.
+  return 0;
+}
+
+int RsaMethodSign(int type,
+                  const unsigned char* message,
+                  unsigned int message_len,
+                  unsigned char* signature,
+                  unsigned int* signature_len,
+                  const RSA* rsa) {
+  // This is only used for client certificate support, which
+  // will always pass the NID_md5_sha1 |type| value.
+  DCHECK_EQ(NID_md5_sha1, type);
+  if (type != NID_md5_sha1) {
+    RSAerr(RSA_F_RSA_SIGN, RSA_R_UNKNOWN_ALGORITHM_TYPE);
+    return 0;
+  }
+  // Retrieve private key JNI reference.
+  jobject private_key = reinterpret_cast<jobject>(RSA_get_app_data(rsa));
+  if (!private_key) {
+    LOG(WARNING) << "Null JNI reference passed to RsaMethodSign!";
+    return 0;
+  }
+  // Sign message with it through JNI.
+  base::StringPiece message_piece(reinterpret_cast<const char*>(message),
+                                  static_cast<size_t>(message_len));
+  std::vector<uint8> result;
+
+  if (!RawSignDigestWithPrivateKey(
+      private_key, message_piece, &result)) {
+    LOG(WARNING) << "Could not sign message in RsaMethodSign!";
+    return 0;
+  }
+
+  size_t expected_size = static_cast<size_t>(RSA_size(rsa));
+  if (result.size() > expected_size) {
+    LOG(ERROR) << "RSA Signature size mismatch, actual: "
+               <<  result.size() << ", expected <= " << expected_size;
+    return 0;
+  }
+
+  // Copy result to OpenSSL-provided buffer
+  memcpy(signature, &result[0], result.size());
+  *signature_len = static_cast<unsigned int>(result.size());
+  return 1;
+}
+
+const RSA_METHOD android_rsa_method = {
+  /* .name = */ "Android signing-only RSA method",
+  /* .rsa_pub_enc = */ RsaMethodPubEnc,
+  /* .rsa_pub_dec = */ RsaMethodPubDec,
+  /* .rsa_priv_enc = */ RsaMethodPrivEnc,
+  /* .rsa_priv_dec = */ RsaMethodPrivDec,
+  /* .rsa_mod_exp = */ NULL,
+  /* .bn_mod_exp = */ NULL,
+  /* .init = */ RsaMethodInit,
+  /* .finish = */ RsaMethodFinish,
+  // This flag is necessary to tell OpenSSL to avoid checking the content
+  // (i.e. internal fields) of the private key. Otherwise, it will complain
+  // it's not valid for the certificate.
+  /* .flags = */ RSA_METHOD_FLAG_NO_CHECK,

[digit1, 2013/02/07 17:29:03]

Fyi, this issue was detected through manual testing (and a bit of OpenSSL
spelunking :-)).

+  /* .app_data = */ NULL,
+  /* .rsa_sign = */ RsaMethodSign,
+  /* .rsa_verify = */ NULL,
+  /* .rsa_keygen = */ NULL,
+};
+
+// Copy the contents of an encoded big integer into an existing BIGNUM.
+// This function modifies |*num| in-place.
+// |new_bytes| is the byte encoding of the new value.
+// |num| points to the BIGNUM which will be assigned with the new value.
+// Returns true on success, false otherwise. On failure, |*num| is
+// not modified.
+bool CopyBigNumFromBytes(const std::vector<uint8>& new_bytes,
+                         BIGNUM* num) {
+  BIGNUM* ret = BN_bin2bn(
+      reinterpret_cast<const unsigned char*>(&new_bytes[0]),
+      static_cast<int>(new_bytes.size()),
+      num);
+  return (ret != NULL);
+}
+
+// Decode the contents of an encoded big integer and either create a new
+// BIGNUM object (if |*num_ptr| is NULL on input) or copy it (if
+// |*num_ptr| is not NULL).
+// |new_bytes| is the byte encoding of the new value.
+// |num_ptr| is the address of a BIGNUM pointer. |*num_ptr| can be NULL.
+// Returns true on success, false otherwise. On failure, |*num_ptr| is
+// not modified. On success, |*num_ptr| will always be non-NULL and
+// point to a valid BIGNUM object.
+bool SwapBigNumPtrFromBytes(const std::vector<uint8>& new_bytes,
+                            BIGNUM** num_ptr) {
+  BIGNUM* old_num = *num_ptr;
+  BIGNUM* new_num = BN_bin2bn(
+      reinterpret_cast<const unsigned char*>(&new_bytes[0]),
+      static_cast<int>(new_bytes.size()),
+      old_num);
+  if (new_num == NULL)
+    return false;
+
+  if (old_num == NULL)
+    *num_ptr = new_num;
+  return true;
+}
+
+// Setup an EVP_PKEY to wrap an existing platform RSA PrivateKey object.
+// |private_key| is the JNI reference (local or global) to the object.
+// |pkey| is the EVP_PKEY to setup as a wrapper.
+// Returns true on success, false otherwise.
+// On success, this creates a new global JNI reference to the object
+// that is owned by and destroyed with the EVP_PKEY. I.e. caller can
+// free |private_key| after the call.
+// IMPORTANT: The EVP_PKEY will *only* work on Android >= 4.2. For older
+// platforms, use GetRsaLegacyKey() instead.
+bool GetRsaPkeyWrapper(jobject private_key, EVP_PKEY* pkey) {
+  ScopedRSA rsa(RSA_new());
+  RSA_set_method(rsa.get(), &android_rsa_method);
+
+  // HACK: RSA_size() doesn't work with custom RSA_METHODs. To ensure that
+  // it will return the right value, set the 'n' field of the RSA object
+  // to match the private key's modulus.
+  std::vector<uint8> modulus;
+  if (!GetRSAKeyModulus(private_key, &modulus)) {
+    LOG(ERROR) << "Failed to get private key modulus";
+    return false;
+  }
+  if (!SwapBigNumPtrFromBytes(modulus, &rsa.get()->n)) {
+    LOG(ERROR) << "Failed to decode private key modulus";
+    return false;
+  }
+
+  ScopedJavaGlobalRef<jobject> global_key;
+  global_key.Reset(NULL, private_key);
+  if (global_key.is_null()) {
+    LOG(ERROR) << "Could not create global JNI reference";
+    return false;
+  }
+  RSA_set_app_data(rsa.get(), global_key.Release());
+  EVP_PKEY_assign_RSA(pkey, rsa.release());
+  return true;
+}
+
+// Setup an EVP_PKEY to wrap an existing platform RSA PrivateKey object
+// for Android 4.0 to 4.1.x. Must only be used on Android < 4.2.
+// |private_key| is a JNI reference (local or global) to the object.
+// |pkey| is the EVP_PKEY to setup as a wrapper.
+// Returns true on success, false otherwise.
+EVP_PKEY* GetRsaLegacyKey(jobject private_key) {
+  EVP_PKEY* sys_pkey =
+      GetOpenSSLSystemHandleForPrivateKey(private_key);
+  if (sys_pkey != NULL) {
+    CRYPTO_add(&sys_pkey->references, 1, CRYPTO_LOCK_EVP_PKEY);
+  } else {
+    // GetOpenSSLSystemHandleForPrivateKey() will fail on Android
+    // 4.0.3 and earlier. However, it is possible to get the key
+    // content with PrivateKey.getEncoded() on these platforms.
+    // Note that this method may return NULL on 4.0.4 and later.
+    std::vector<uint8> encoded;
+    if (!GetPrivateKeyEncodedBytes(private_key, &encoded)) {
+      LOG(ERROR) << "Can't get private key data!";
+      return NULL;
+    }
+    const unsigned char* p =
+        reinterpret_cast<const unsigned char*>(&encoded[0]);
+    int len = static_cast<int>(encoded.size());
+    sys_pkey = d2i_AutoPrivateKey(NULL, &p, len);
+    if (sys_pkey == NULL) {
+      LOG(ERROR) << "Can't convert private key data!";
+      return NULL;
+    }
+  }
+  return sys_pkey;
+}
+
+// Custom DSA_METHOD that uses the platform APIs.
+// Note that for now, only signing through DSA_sign() is really supported.
+// all other method pointers are either stubs returning errors, or no-ops.
+// See <openssl/dsa.h> for exact declaration of DSA_METHOD.
+//
+// Note: There is no DSA_set_app_data() and DSA_get_app_data() functions,
+//       but RSA_set_app_data() is defined as a simple macro that calls
+//       RSA_set_ex_data() with a hard-coded index of 0, so this code
+//       does the same thing here.
+
+DSA_SIG* DsaMethodDoSign(const unsigned char* dgst,
+                         int dlen,
+                         DSA* dsa) {
+  // Extract the JNI reference to the PrivateKey object.
+  jobject private_key = reinterpret_cast<jobject>(DSA_get_ex_data(dsa, 0));
+  if (private_key == NULL)
+    return NULL;
+
+  // Sign the message with it, calling platform APIs.
+  std::vector<uint8> signature;
+  if (!RawSignDigestWithPrivateKey(
+        private_key,
+        base::StringPiece(
+            reinterpret_cast<const char*>(dgst),
+            static_cast<size_t>(dlen)),
+        &signature)) {

[Ryan Sleevi, 2013/02/08 22:43:32]

style nit: still wrong

if (!RawSignDigestWithPrivateKey(
        private_key,
        base::StringPiece(
            ...

[digit1, 2013/02/11 09:05:56]

Oh damn, done. thanks.

+    return NULL;
+  }
+
+  // Note: With DSA, the actual signature might be smaller than DSA_size().
+  size_t max_expected_size = static_cast<size_t>(DSA_size(dsa));
+  if (signature.size() > max_expected_size) {
+    LOG(ERROR) << "DSA Signature size mismatch, actual: "
+               << signature.size() << ", expected <= "
+               << max_expected_size;
+    return NULL;
+  }
+
+  // Convert the signature into a DSA_SIG object.
+  const unsigned char* sigbuf =
+      reinterpret_cast<const unsigned char*>(&signature[0]);
+  int siglen = static_cast<size_t>(signature.size());
+  DSA_SIG* dsa_sig = d2i_DSA_SIG(NULL, &sigbuf, siglen);
+  return dsa_sig;
+}
+
+int DsaMethodSignSetup(DSA* dsa,
+                       BN_CTX* ctx_in,
+                       BIGNUM** kinvp,
+                       BIGNUM** rp) {
+  NOTIMPLEMENTED();
+  DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_INVALID_DIGEST_TYPE);
+  return -1;
+}
+
+int DsaMethodDoVerify(const unsigned char* dgst,
+                      int dgst_len,
+                      DSA_SIG* sig,
+                      DSA* dsa) {
+  NOTIMPLEMENTED();
+  DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_INVALID_DIGEST_TYPE);
+  return -1;
+}
+
+int DsaMethodFinish(DSA* dsa) {
+  // Free the global JNI reference.
+  jobject key = reinterpret_cast<jobject>(DSA_get_ex_data(dsa,0));
+  if (key != NULL) {
+    DSA_set_ex_data(dsa, 0, NULL);
+    JNIEnv* env = base::android::AttachCurrentThread();
+    env->DeleteGlobalRef(key);
+  }
+  // Actual return value is ignored by OpenSSL. There are no docs
+  // explaining what this is supposed to be.
+  return 0;
+}
+
+const DSA_METHOD android_dsa_method = {
+  /* .name = */ "Android signing-only DSA method",
+  /* .dsa_do_sign = */ DsaMethodDoSign,
+  /* .dsa_sign_setup = */ DsaMethodSignSetup,
+  /* .dsa_do_verify = */ DsaMethodDoVerify,
+  /* .dsa_mod_exp = */ NULL,
+  /* .bn_mod_exp = */ NULL,
+  /* .init = */ NULL,  // nothing to do here.
+  /* .finish = */ DsaMethodFinish,
+  /* .flags = */ 0,
+  /* .app_data = */ NULL,
+  /* .dsa_paramgem = */ NULL,
+  /* .dsa_keygen = */ NULL
+};
+
+// Setup an EVP_PKEY to wrap an existing DSA platform PrivateKey object.
+// |private_key| is a JNI reference (local or global) to the object.
+// |pkey| is the EVP_PKEY to setup as a wrapper.
+// Returns true on success, false otherwise.
+// On success, this creates a global JNI reference to the same object
+// that will be owned by and destroyed with the EVP_PKEY.
+bool GetDsaPkeyWrapper(jobject private_key, EVP_PKEY* pkey) {
+  ScopedDSA dsa(DSA_new());
+  DSA_set_method(dsa.get(), &android_dsa_method);
+
+  // DSA_size() doesn't work with custom DSA_METHODs. To ensure it
+  // returns the right value, set the 'q' field in the DSA object to
+  // match the parameter from the platform key.
+  std::vector<uint8> q;
+  if (!GetDSAKeyParamQ(private_key, &q)) {
+    LOG(ERROR) << "Can't extract Q parameter from DSA private key";
+    return false;
+  }
+  if (!SwapBigNumPtrFromBytes(q, &dsa.get()->q)) {
+    LOG(ERROR) << "Can't decode Q parameter from DSA private key";
+    return false;
+  }
+
+  ScopedJavaGlobalRef<jobject> global_key;
+  global_key.Reset(NULL, private_key);
+  if (global_key.is_null()) {
+    LOG(ERROR) << "Could not create global JNI reference";
+    return false;
+  }
+  DSA_set_ex_data(dsa.get(), 0, global_key.Release());
+  EVP_PKEY_assign_DSA(pkey, dsa.release());
+  return true;
+}
+
+// Custom ECDSA_METHOD that uses the platform APIs.
+// Note that for now, only signing through ECDSA_sign() is really supported.
+// all other method pointers are either stubs returning errors, or no-ops.
+//
+// Note: The ECDSA_METHOD structure doesn't have init/finish
+//       methods. As such, the only way to to ensure the global
+//       JNI reference is properly released when the EVP_PKEY is
+//       destroyed is to use a custom EX_DATA type.
+
+// Used to ensure that the global JNI reference associated with a
+// custom EC_KEY + ECDSA_METHOD is released when the key is destroyed.
+void ExDataFree(void* parent,
+                void* ptr,
+                CRYPTO_EX_DATA* ad,
+                int idx,
+                long argl,
+                void* argp) {
+  jobject private_key = reinterpret_cast<jobject>(ptr);
+  if (private_key == NULL)
+    return;
+
+  CRYPTO_set_ex_data(ad, idx, NULL);
+
+  JNIEnv* env = base::android::AttachCurrentThread();
+  env->DeleteGlobalRef(private_key);
+}
+
+int ExDataDup(CRYPTO_EX_DATA* to,
+              CRYPTO_EX_DATA* from,
+              void* from_d,
+              int idx,
+              long argl,
+              void* argp) {
+  // This callback shall never be called with the current OpenSSL
+  // implementation (the library only ever duplicates EX_DATA items
+  // for SSL and BIO objects). But provide this to catch regressions
+  // in the future.
+  CHECK(false) << "ExDataDup was called for ECDSA custom key !?";
+  // Return value is currently ignored by OpenSSL.
+  return 0;
+}
+
+class EcdsaExDataIndex {
+public:
+  int ex_data_index() { return ex_data_index_; }
+
+  EcdsaExDataIndex() {
+    ex_data_index_ = ECDSA_get_ex_new_index(0,           // argl
+                                            NULL,        // argp
+                                            NULL,        // new_func
+                                            ExDataDup,   // dup_func
+                                            ExDataFree); // free_func
+  }
+
+private:
+  int ex_data_index_;
+};
+
+// Returns the index of the custom EX_DATA used to store the JNI reference.
+int EcdsaGetExDataIndex(void) {
+  // Use a LazyInstance to perform thread-safe lazy initialization.
+  // Use a leaky one, since OpenSSL doesn't provide a way to release
+  // allocated EX_DATA indices.
+  static base::LazyInstance<EcdsaExDataIndex>::Leaky s_instance =
+      LAZY_INSTANCE_INITIALIZER;
+  return s_instance.Get().ex_data_index();
+}
+
+ECDSA_SIG* EcdsaMethodDoSign(const unsigned char* dgst,
+                             int dgst_len,
+                             const BIGNUM* inv,
+                             const BIGNUM* rp,
+                             EC_KEY* eckey) {
+  // Retrieve private key JNI reference.
+  jobject private_key = reinterpret_cast<jobject>(
+      ECDSA_get_ex_data(eckey, EcdsaGetExDataIndex()));
+  if (!private_key) {
+    LOG(WARNING) << "Null JNI reference passed to EcdsaMethodDoSign!";
+    return NULL;
+  }
+  // Sign message with it through JNI.
+  std::vector<uint8> signature;
+  base::StringPiece digest(
+      reinterpret_cast<const char*>(dgst),
+      static_cast<size_t>(dgst_len));
+  if (!RawSignDigestWithPrivateKey(
+          private_key, digest, &signature)) {
+    LOG(WARNING) << "Could not sign message in EcdsaMethodDoSign!";
+    return NULL;
+  }
+
+  // Note: With ECDSA, the actual signature may be smaller than
+  // ECDSA_size().
+  size_t max_expected_size = static_cast<size_t>(ECDSA_size(eckey));
+  if (signature.size() > max_expected_size) {
+    LOG(ERROR) << "ECDSA Signature size mismatch, actual: "
+               <<  signature.size() << ", expected <= "
+               << max_expected_size;
+    return NULL;
+  }
+
+  // Convert signature to ECDSA_SIG object
+  const unsigned char* sigbuf =
+      reinterpret_cast<const unsigned char*>(&signature[0]);
+  long siglen = static_cast<long>(signature.size());
+  return d2i_ECDSA_SIG(NULL, &sigbuf, siglen);
+}
+
+int EcdsaMethodSignSetup(EC_KEY* eckey,
+                         BN_CTX* ctx,
+                         BIGNUM** kinv,
+                         BIGNUM** r) {
+  NOTIMPLEMENTED();
+  ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ECDSA_R_ERR_EC_LIB);
+  return -1;
+}
+
+int EcdsaMethodDoVerify(const unsigned char* dgst,
+                        int dgst_len,
+                        const ECDSA_SIG* sig,
+                        EC_KEY* eckey) {
+  NOTIMPLEMENTED();
+  ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ECDSA_R_ERR_EC_LIB);
+  return -1;
+}
+
+const ECDSA_METHOD android_ecdsa_method = {
+  /* .name = */ "Android signing-only ECDSA method",
+  /* .ecdsa_do_sign = */ EcdsaMethodDoSign,
+  /* .ecdsa_sign_setup = */ EcdsaMethodSignSetup,
+  /* .ecdsa_do_verify = */ EcdsaMethodDoVerify,
+  /* .flags = */ 0,
+  /* .app_data = */ NULL,
+};
+
+// Setup an EVP_PKEY to wrap an existing platform PrivateKey object.
+// |private_key| is the JNI reference (local or global) to the object.
+// |pkey| is the EVP_PKEY to setup as a wrapper.
+// Returns true on success, false otherwise.
+// On success, this creates a global JNI reference to the object that
+// is owned by and destroyed with the EVP_PKEY. I.e. the caller shall
+// always free |private_key| after the call.
+bool GetEcdsaPkeyWrapper(jobject private_key, EVP_PKEY* pkey) {
+  ScopedEC_KEY eckey(EC_KEY_new());
+  ECDSA_set_method(eckey.get(), &android_ecdsa_method);
+
+  // To ensure that ECDSA_size() works properly, craft a custom EC_GROUP
+  // that has the same order than the private key.
+  std::vector<uint8> order;
+  if (!GetECKeyOrder(private_key, &order)) {
+    LOG(ERROR) << "Can't extract order parameter from EC private key";
+    return false;
+  }
+  ScopedEC_GROUP group(EC_GROUP_new(EC_GFp_nist_method()));
+  if (!group.get()) {
+    LOG(ERROR) << "Can't create new EC_GROUP";
+    return false;
+  }
+  if (!CopyBigNumFromBytes(order, &group.get()->order)) {
+    LOG(ERROR) << "Can't decode order from PrivateKey";
+    return false;
+  }
+  EC_KEY_set_group(eckey.get(), group.release());
+
+  ScopedJavaGlobalRef<jobject> global_key;
+  global_key.Reset(NULL, private_key);
+  if (global_key.is_null()) {
+    LOG(ERROR) << "Can't create global JNI reference";
+    return false;
+  }
+  ECDSA_set_ex_data(eckey.get(),
+                    EcdsaGetExDataIndex(),
+                    global_key.Release());
+
+  EVP_PKEY_assign_EC_KEY(pkey, eckey.release());
+  return true;
+}
+
+}  // namespace
+
+EVP_PKEY* GetOpenSSLPrivateKeyWrapper(jobject private_key) {
+  // Create new empty EVP_PKEY instance.
+  ScopedEVP_PKEY pkey(EVP_PKEY_new());
+  if (!pkey.get())
+    return NULL;
+
+  // Create sub key type, depending on private key's algorithm type.
+  PrivateKeyType key_type = GetPrivateKeyType(private_key);
+  switch (key_type) {
+    case PRIVATE_KEY_TYPE_RSA:
+      {
+        // Route around platform bug: if Android < 4.2, then
+        // base::android::RawSignDigestWithPrivateKey() cannot work, so
+        // instead, obtain a raw EVP_PKEY* to the system object
+        // backing this PrivateKey object.
+        const int kAndroid42ApiLevel = 17;
+        if (base::android::BuildInfo::GetInstance()->sdk_int() <
+            kAndroid42ApiLevel) {
+          EVP_PKEY* legacy_key = GetRsaLegacyKey(private_key);
+          if (legacy_key == NULL)
+            return NULL;
+          pkey.reset(legacy_key);
+        } else {
+          // Running on Android 4.2.
+          if (!GetRsaPkeyWrapper(private_key, pkey.get()))
+            return NULL;
+        }
+      }
+      break;
+    case PRIVATE_KEY_TYPE_DSA:
+      if (!GetDsaPkeyWrapper(private_key, pkey.get()))
+        return NULL;
+      break;
+    case PRIVATE_KEY_TYPE_ECDSA:
+      if (!GetEcdsaPkeyWrapper(private_key, pkey.get()))
+        return NULL;
+      break;
+    default:
+      LOG(WARNING)
+          << "GetOpenSSLPrivateKeyWrapper() called with invalid key type";
+      return NULL;
+  }
+  return pkey.release();
+}
+
+}  // namespace android
+}  // namespace net