Merge pull request #54 from EdgeApp/william/fix-length-math

Fix length math

Author: swansontec

CHANGELOG.md

@@ -1,5 +1,9 @@
 # react-native-fast-crypto
 
+## Unreleased
+
+- fixed: Malloc proper size for secp256k1 keys.
+
 ## 2.2.0 (2022-03-18)
 
 - changed: Compile secp256k1 as an XCFramework, making it compatible with the iOS simulator on M1 Macs.

android/src/main/cpp/crypto_bridge.cpp

@@ -1,7 +1,7 @@
 //fastCrypto.cpp
 #include <android/log.h>
 #include <jni.h>
-#include "fast_crypto.h"
+#include "native-crypto.h"
 
 #define LOG_TAG "crypto_bridge-JNI"
 
@@ -292,9 +292,8 @@ Java_co_airbitz_fastcrypto_RNFastCryptoModule_secp256k1EcPubkeyCreateJNI(JNIEnv
     }
     int privateKeyLen = strlen(szPrivateKeyHex);
 
-    // Buffer size: privateKeyLen * 2 + 3 bytes
-    // For 64-char private key: uncompressed public key = 130 hex chars (string) + 1 null terminator = 131 bytes
-    char szPublicKeyHex[privateKeyLen * 2 + 3];
+    // Hex with a null terminator is 2 * bytes + 1:
+    char szPublicKeyHex[2 * DECOMPRESSED_PUBKEY_LENGTH + 1];
 
     fast_crypto_secp256k1_ec_pubkey_create(szPrivateKeyHex, szPublicKeyHex, jiCompressed);
     jstring out = env->NewStringUTF(szPublicKeyHex);

android/src/main/cpp/fast_crypto.h

@@ -16,10 +16,6 @@ extern "C" {
 #include <stdlib.h>
 #include <string.h>
 
-#define COMPRESSED_PUBKEY_LENGTH 33
-#define DECOMPRESSED_PUBKEY_LENGTH 65
-#define PRIVKEY_LENGTH 64
-
 void fast_crypto_scrypt (const uint8_t *passwd, size_t passwdlen, const uint8_t *salt, size_t saltlen, uint64_t N,
     uint32_t r, uint32_t p, uint8_t *buf, size_t buflen)
 {

android/src/main/cpp/native-crypto.cpp

@@ -44,6 +44,10 @@
 extern "C" {
 #endif
 
+#define COMPRESSED_PUBKEY_LENGTH 33
+#define DECOMPRESSED_PUBKEY_LENGTH 65
+#define PRIVKEY_LENGTH 64
+
 void fast_crypto_scrypt (const uint8_t *passwd, size_t passwdlen, const uint8_t *salt, size_t saltlen, uint64_t N,
     uint32_t r, uint32_t p, uint8_t *buf, size_t buflen);
 void fast_crypto_secp256k1_ec_privkey_tweak_add(char *szPrivateKeyHex, const char *szTweak);

android/src/main/cpp/native-crypto.h

@@ -79,12 +79,10 @@ - (dispatch_queue_t)methodQueue
                  resolver:(RCTPromiseResolveBlock)resolve
                  rejecter:(RCTPromiseRejectBlock)reject)
 {
-  // Buffer size: privateKeyLen * 2 + 3 bytes
-  // For 64-char private key: uncompressed public key = 130 hex chars (string) + 1 null terminator = 131 bytes
-  char *szPublicKeyHex = malloc(sizeof(char) * ([privateKeyHex length] * 2 + 3)); 
+  // Hex with a null terminator is 2 * bytes + 1:
+  char szPublicKeyHex[2 * DECOMPRESSED_PUBKEY_LENGTH + 1];
   fast_crypto_secp256k1_ec_pubkey_create([privateKeyHex UTF8String], szPublicKeyHex, compressed);
   NSString *publicKeyHex = [NSString stringWithUTF8String:szPublicKeyHex];
-  free(szPublicKeyHex);
   resolve(publicKeyHex);
 }