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crypto: add HMAC to crypto.timingSafeEqual() #38488

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crypto: add HMAC to crypto.timingSafeEqual() #38488

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43 changes: 42 additions & 1 deletion src/crypto/crypto_timing.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@
#include "node.h"

#include <openssl/crypto.h>
#include <openssl/hmac.h>
#include <openssl/sha.h>

namespace node {

Expand Down Expand Up @@ -42,8 +44,47 @@ void TimingSafeEqual(const FunctionCallbackInfo<Value>& args) {
return;
}

uint16_t bufKey[8];
CHECK(crypto::EntropySource(reinterpret_cast<unsigned char*>(bufKey),
sizeof(bufKey)));
char key[kKeySize];
snprintf(key,
sizeof(key),
"%04x%04x%04x%04x%04x%04x%04x%04x",
bufKey[0],
bufKey[1],
bufKey[2],
bufKey[3],
bufKey[4],
bufKey[5],
bufKey[6],
bufKey[7]);

std::array<unsigned char, EVP_MAX_MD_SIZE> hash1;
std::array<unsigned char, EVP_MAX_MD_SIZE> hash2;
Comment on lines +63 to +64
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why not just unsigned char hash1[EVP_MAX_MD_SIZE] here?

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Sure, I don't know the difference, so that works for me. 😬

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Afaik, C-style array lacks the higher-level functionalities of std::array, hence, they do not track their own size, so you need to manage size information manually. So for this particular case, I think it's better to keep std::array , since we keeps track of arrays own size.

unsigned int hash1Len;
unsigned int hash2Len;

HMAC(EVP_sha256(),
key,
kKeySize,
reinterpret_cast<unsigned char const*>(buf1.data()),
static_cast<int>(buf1.size()),
hash1.data(),
&hash1Len);

HMAC(EVP_sha256(),
key,
kKeySize,
reinterpret_cast<unsigned char const*>(buf2.data()),
static_cast<int>(buf2.size()),
hash2.data(),
&hash2Len);

assert(hash1Len == hash2Len);

return args.GetReturnValue().Set(
CRYPTO_memcmp(buf1.data(), buf2.data(), buf1.size()) == 0);
CRYPTO_memcmp(hash1.data(), hash2.data(), hash1Len) == 0);
}

void Initialize(Environment* env, Local<Object> target) {
Expand Down
3 changes: 3 additions & 0 deletions src/crypto/crypto_timing.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,9 @@ namespace crypto {
namespace Timing {
void Initialize(Environment* env, v8::Local<v8::Object> target);
void RegisterExternalReferences(ExternalReferenceRegistry* registry);

static const int kKeySize = 256;

} // namespace Timing
} // namespace crypto
} // namespace node
Expand Down