Use SHA256 bytes without translating to string

src/main/kotlin/com/klaxit/hiddensecrets/Utils.kt

@@ -26,20 +26,19 @@ object Utils {
      * Encode string to sha256
      */
     @VisibleForTesting
-    fun sha256(toHash: String): String {
+    fun sha256(toHash: String): ByteArray {
         val bytes = toHash.toByteArray()
         val md = MessageDigest.getInstance("SHA-256")
         val digest = md.digest(bytes)
-        return digest.fold("") { str, it -> str + "%02x".format(it) }
+        return digest
     }
 
     /**
      * Encode a string key to and hex array using package name
      */
     fun encodeSecret(key: String, packageName: String): String {
         // Generate the obfuscator as the SHA256 of the app package name
-        val obfuscator = sha256(packageName)
-        val obfuscatorBytes = obfuscator.toByteArray()
+        val obfuscatorBytes = sha256(packageName)
 
         // Generate the obfuscated secret bytes array by applying a XOR between the secret and the obfuscator
         val obfuscatedSecretBytes = arrayListOf<Byte>()

src/main/resources/cpp/secrets.cpp

@@ -45,15 +45,15 @@ jstring getOriginalKey(
 
     // Get the obfuscating string SHA256 as the obfuscator
     const char *obfuscatingStr = pEnv->GetStringUTFChars(obfuscatingJStr, NULL);
-    char buffer[2 * SHA256::DIGEST_SIZE + 1];
+    char buffer[SHA256::DIGEST_SIZE];
 
     sha256(obfuscatingStr, buffer);
     const char *obfuscator = buffer;
 
     // Apply a XOR between the obfuscated key and the obfuscating string to get original string
     char out[obfuscatedSecretSize + 1];
     for (int i = 0; i < obfuscatedSecretSize; i++) {
-        out[i] = obfuscatedSecret[i] ^ obfuscator[i % strlen(obfuscator)];
+        out[i] = obfuscatedSecret[i] ^ obfuscator[i % SHA256::DIGEST_SIZE];
     }
 
     // Add string terminal delimiter

src/main/resources/cpp/sha256.cpp

@@ -150,7 +150,7 @@ void SHA256::final(unsigned char *digest)
     }
 }
 
-void sha256(const char* input, char buf[2*SHA256::DIGEST_SIZE + 1])
+void sha256(const char* input, char buf[SHA256::DIGEST_SIZE])
 {
     unsigned char digest[SHA256::DIGEST_SIZE];
     memset(digest, 0, SHA256::DIGEST_SIZE);
@@ -160,9 +160,6 @@ void sha256(const char* input, char buf[2*SHA256::DIGEST_SIZE + 1])
     ctx.update( (unsigned char*)input, strlen(input));
     ctx.final(digest);
 
-    buf[2*SHA256::DIGEST_SIZE] = 0;
-    for (int i = 0; i < SHA256::DIGEST_SIZE; i++) {
-        sprintf(buf + i * 2, "%02x", digest[i]);
-    }
+    memcpy(buf, digest, SHA256::DIGEST_SIZE);
 }
 

src/test/kotlin/HiddenSecretsTest.kt

@@ -45,7 +45,7 @@ class HiddenSecretsTest : WordSpec({
             val result = gradleRunner.withArguments(HiddenSecretsPlugin.TASK_OBFUSCATE, "-Pkey=$key", "-Ppackage=$packageName").build()
             println(result.output)
             // Should contain obfuscated key
-            result.output shouldContain "{ 0x15, 0x58, 0xb, 0x43, 0x78, 0x4a, 0x23, 0x6d, 0x1, 0x4b, 0x46, 0x7c, 0x57, 0x41 }"
+            result.output shouldContain "{ 0xd4, 0xd8, 0x70, 0xca, 0x91, 0x54, 0x69, 0x77, 0xc4, 0xb6, 0x99, 0x5f, 0xb8, 0x98 }"
         }
 
         "Make command ${HiddenSecretsPlugin.TASK_PACKAGE_NAME} succeed" {

src/test/kotlin/UtilsTest.kt

@@ -8,6 +8,8 @@ import java.io.File
  */
 class UtilsTest : WordSpec({
 
+    fun byteArrayOfInts(vararg ints: Int) = ByteArray(ints.size) { pos -> ints[pos].toByte() }
+
     val packageName = "com.klaxit.test"
 
     "Using getCppPackageName()" should {
@@ -25,7 +27,7 @@ class UtilsTest : WordSpec({
     "Using sha256()" should {
         "encode String in sha256" {
             val key = "youCanNotFindMySecret!"
-            Utils.sha256(key) shouldBe "7bdc2b5992ef7b4cce0e06295f564f4fad0c96e5f82a0bcf9cd8323d3a3bcfbd"
+            Utils.sha256(key) shouldBe byteArrayOfInts( 0x7b, 0xdc, 0x2b, 0x59, 0x92, 0xef, 0x7b, 0x4c, 0xce, 0x0e, 0x06, 0x29, 0x5f, 0x56, 0x4f, 0x4f, 0xad, 0x0c, 0x96, 0xe5, 0xf8, 0x2a, 0x0b, 0xcf, 0x9c, 0xd8, 0x32, 0x3d, 0x3a, 0x3b, 0xcf, 0xbd) /*"7bdc2b5992ef7b4cce0e06295f564f4fad0c96e5f82a0bcf9cd8323d3a3bcfbd"*/
         }
     }
 
@@ -35,14 +37,14 @@ class UtilsTest : WordSpec({
             Utils.encodeSecret(
                 key,
                 packageName
-            ) shouldBe "{ 0x5b, 0x6, 0x18, 0x31, 0xb, 0x72, 0x57, 0x5, 0x5d, 0x57, 0x3 }"
+            ) shouldBe "{ 0x67, 0xcb, 0xae, 0xcb, 0x4c, 0xbb, 0x42, 0xad, 0x59, 0x19, 0xe2 }" //"{ 0x5b, 0x6, 0x18, 0x31, 0xb, 0x72, 0x57, 0x5, 0x5d, 0x57, 0x3 }"
         }
         "encode String with special characters" {
             val key = "@&é(§èçà)-ù,;:=#°_*%£?./+"
             Utils.encodeSecret(
                 key,
                 packageName
-            ) shouldBe "{ 0x70, 0x45, 0xa2, 0xcc, 0x4c, 0xf5, 0x9e, 0xa5, 0x9a, 0xf0, 0xc1, 0xa6, 0x92, 0x4a, 0x4e, 0xa6, 0x8a, 0x1a, 0xc, 0x5e, 0x5, 0x14, 0xf7, 0x86, 0x6b, 0x13, 0x40, 0xf5, 0x9a, 0xc, 0x16, 0x16, 0x19 }"
+            ) shouldBe "{ 0x4c, 0x88, 0x14, 0x36, 0xb, 0x3c, 0x8b, 0xd, 0x9e, 0xbe, 0x20, 0x95, 0xe9, 0xce, 0xbe, 0x4a, 0x94, 0xf1, 0xb2, 0x7d, 0x4c, 0x70, 0x51, 0x91, 0x69, 0x98, 0x4d, 0xf7, 0x8a, 0xbc, 0xb1, 0xa2, 0x27 }"
         }
     }