OpenSSL: EC_POINT_set_compressed_coordinates_GFp分段故障

Question

使用gdb试图找出分段错误(实际上没有帮助)，但我可能传递了错误的参数。下面是代码和回溯：

echd.cc

#include <node.h>
#include <nan.h>
#include <openssl/evp.h>
#include <openssl/ec.h>

using v8::Handle;
using v8::FunctionTemplate;
using v8::Object;
using v8::String;

static const size_t PRIVKEY_SIZE = 32;
static const size_t PUBKEY_SIZE = 65;
static const size_t COMPRESSED_PUBKEY_SIZE = 33;

#define CHECK(cond) do { if (!(cond)) goto error; } while (0)

int derive(const uint8_t* privkey_a, const uint8_t* pubkey_b, uint8_t* shared) {
  int rc = -1;
  int res;
  BIGNUM* pkey_bn = NULL;
  EC_KEY* pkey = NULL;
  bool compressed = false;
  EC_KEY* peerkey = NULL;
  int compressed_y_bit = 0;
  EC_POINT* peerkey_p = NULL;
  const EC_GROUP* peerkey_group = NULL;
  BN_CTX* peerkey_ctx = NULL;
  BIGNUM* peerkey_bn = NULL;
  BIGNUM* peerkey_bn_x = NULL;
  BIGNUM* peerkey_bn_y = NULL;
  EVP_PKEY* evp_pkey = NULL;
  EVP_PKEY* evp_peerkey = NULL;
  EVP_PKEY_CTX* ctx = NULL;
  size_t shared_len = PRIVKEY_SIZE;

  // Private key A.
  CHECK((pkey_bn = BN_bin2bn(privkey_a, PRIVKEY_SIZE, NULL)) != NULL);
  CHECK((pkey = EC_KEY_new_by_curve_name(NID_secp256k1)) != NULL);
  CHECK(EC_KEY_set_private_key(pkey, pkey_bn) == 1);
  CHECK((evp_pkey = EVP_PKEY_new()) != NULL);
  CHECK(EVP_PKEY_set1_EC_KEY(evp_pkey, pkey) == 1);

  // Public key B.
  CHECK((peerkey = EC_KEY_new_by_curve_name(NID_secp256k1)) != NULL);
  (pubkey_b[0] == 2 || pubkey_b[0] == 3) ? compressed = true : compressed = false;
  if (compressed) {
    (pubkey_b[0] == 2) ? compressed_y_bit = 0 : compressed_y_bit = 1;
    CHECK((peerkey_group = EC_KEY_get0_group(peerkey)) != NULL);
    CHECK((peerkey_ctx = BN_CTX_new()) != NULL);
    CHECK((peerkey_bn = BN_bin2bn(pubkey_b+1, COMPRESSED_PUBKEY_SIZE, NULL)) != NULL);
    CHECK((EC_POINT_set_compressed_coordinates_GFp(peerkey_group,
                                                 peerkey_p,
                                                 peerkey_bn,
                                                 compressed_y_bit,
                                                 NULL)) != NULL);
    ...

回溯

(gdb) bt
#0  0x00000000012097a3 in EC_POINT_set_compressed_coordinates_GFp ()
#1  0x00007ffff4648446 in derive (privkey_a=0x2214af0 '\004' <repeats 32 times>, " \332+\002", pubkey_b=0x2214ec0 "\003\033\204\305V{\022d@\231]>ժ\272\005e\327\036\030\064`H\031\377\234\027\365\351\325\335\a\217\332+\002", shared=0x222d5d0 " c,\002") at ../ecdh.cc:51
#2  0x00007ffff4648817 in Derive (info=...) at ../ecdh.cc:117
#3  0x00007ffff4647756 in Nan::imp::FunctionCallbackWrapper (info=...) at ../node_modules/nan/nan_callbacks_12_inl.h:176
#4  0x0000000000a94a43 in v8::internal::FunctionCallbackArguments::Call(void (*)(v8::FunctionCallbackInfo<v8::Value> const&)) ()
#5  0x0000000000b0bbec in v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) ()
#6  0x0000000000b0c83f in v8::internal::Builtin_HandleApiCall(int, v8::internal::Object**, v8::internal::Isolate*) ()
#7  0x00002b6f5fe042fd in ?? ()
#8  0x00002b6f5fe04241 in ?? ()
#9  0x00007fffffffc610 in ?? ()
#10 0x0000000000000006 in ?? ()
---Type <return> to continue, or q <return> to quit---q
Quit

Answer 1

调用EC_POINT_set_compressed_coordinates_GFp()中的EC_POINT_set_compressed_coordinates_GFp()参数是NULL，而应该是初始化的EC_POINT *。在调用该函数之前添加类似的内容(为了清晰起见省略检查)：

peerkey_p = EC_POINT_new(peerkey_group);

这样就能排除分段故障。

在使用COMPRESSED_PUBKEY_SIZE等于33时，您似乎又犯了一个错误。是的，公钥的总大小是33字节。但是，在指针pubkey_b按1字节前进之后，只有32字节仍然与BN_bin2bn()函数相关。

此外，EC_POINT_set_compressed_coordinates_GFp()的返回值是int，而不是指针。因此，与其将其与NULL进行比较，不如将其与1的成功值进行比较。