Add BN_bn2binpad API and enable OpenVPN master CI testing

Author: julek-wolfssl

.github/workflows/openvpn.yml

@@ -42,9 +42,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # Pinned refs: avoid OpenVPN master until wolfSSL adds any new OpenSSL
-        # APIs it adopts (e.g. BN_bn2binpad). release/2.6 + latest stable tag.
-        ref: [ release/2.6, v2.6.19 ]
+        ref: [ master, release/2.6, v2.6.19 ]
     name: ${{ matrix.ref }}
     if: github.repository_owner == 'wolfssl'
     runs-on: ubuntu-24.04

src/ssl_bn.c

@@ -468,6 +468,56 @@ int wolfSSL_BN_bn2bin(const WOLFSSL_BIGNUM* bn, unsigned char* r)
 }
 
 
+/* Encode a big number as a big-endian byte array, zero-padded to tolen bytes.
+ *
+ * Returns tolen on success, -1 on error (including when the number is too
+ * large to fit in tolen bytes).
+ *
+ * @param [in]  bn     Big number to encode.
+ * @param [out] r      Buffer to place encoding into. Must be at least tolen
+ *                     bytes.
+ * @param [in]  toLen  Desired output length in bytes.
+ * @return  toLen on success.
+ * @return  -1 on error.
+ */
+int wolfSSL_BN_bn2binpad(const WOLFSSL_BIGNUM* bn, unsigned char* r, int toLen)
+{
+    int numBytes;
+
+    WOLFSSL_ENTER("wolfSSL_BN_bn2binpad");
+
+    /* Validate parameters. */
+    if (BN_IS_NULL(bn) || (r == NULL) || (toLen < 0)) {
+        WOLFSSL_MSG("NULL bn, r, or invalid tolen error");
+        return WOLFSSL_FATAL_ERROR;
+    }
+
+    /* Get the number of bytes needed to encode the big number. */
+    numBytes = mp_unsigned_bin_size((mp_int*)bn->internal);
+    if (numBytes < 0) {
+        WOLFSSL_MSG("mp_unsigned_bin_size error");
+        return WOLFSSL_FATAL_ERROR;
+    }
+    if (numBytes > toLen) {
+        WOLFSSL_MSG("BN too large for tolen");
+        return WOLFSSL_FATAL_ERROR;
+    }
+
+    /* Zero-pad leading bytes. */
+    XMEMSET(r, 0, (size_t)(toLen - numBytes));
+
+    /* Encode the big number into the remaining bytes. */
+    if (numBytes > 0 &&
+        mp_to_unsigned_bin((mp_int*)bn->internal, r + toLen - numBytes) !=
+            MP_OKAY) {
+        WOLFSSL_MSG("mp_to_unsigned_bin error");
+        return WOLFSSL_FATAL_ERROR;
+    }
+
+    return toLen;
+}
+
+
 /* Return a big number with value of the decoding of the big-endian byte array.
  *
  * Returns ret when not NULL.

tests/api/test_ossl_bn.c

@@ -323,6 +323,39 @@ int test_wolfSSL_BN_enc_dec(void)
     ExpectNotNull(BN_bin2bn(binNum, sizeof(binNum), b));
     ExpectIntEQ(BN_cmp(a, b), -1);
 
+    /* BN_bn2binpad tests */
+    {
+        unsigned char padOut[5];
+
+        /* Invalid parameters */
+        ExpectIntEQ(BN_bn2binpad(NULL, padOut, sizeof(padOut)), -1);
+        ExpectIntEQ(BN_bn2binpad(&emptyBN, padOut, sizeof(padOut)), -1);
+        ExpectIntEQ(BN_bn2binpad(a, NULL, sizeof(padOut)), -1);
+        ExpectIntEQ(BN_bn2binpad(a, padOut, -1), -1);
+        /* tolen too small for the value */
+        ExpectNotNull(BN_bin2bn(binNum, sizeof(binNum), b));
+        ExpectIntEQ(BN_bn2binpad(b, padOut, 2), -1);
+        /* Normal case: a = 2, padded to 5 bytes */
+        XMEMSET(padOut, 0xFF, sizeof(padOut));
+        ExpectIntEQ(BN_bn2binpad(a, padOut, 5), 5);
+        ExpectIntEQ(padOut[0], 0x00);
+        ExpectIntEQ(padOut[1], 0x00);
+        ExpectIntEQ(padOut[2], 0x00);
+        ExpectIntEQ(padOut[3], 0x00);
+        ExpectIntEQ(padOut[4], 0x02);
+        /* Exact size (no padding needed) */
+        ExpectIntEQ(BN_bn2binpad(a, padOut, 1), 1);
+        ExpectIntEQ(padOut[0], 0x02);
+        /* Zero value padded to 3 bytes */
+        ExpectIntEQ(BN_set_word(a, 0), 1);
+        ExpectIntEQ(BN_bn2binpad(a, padOut, 3), 3);
+        ExpectIntEQ(padOut[0], 0x00);
+        ExpectIntEQ(padOut[1], 0x00);
+        ExpectIntEQ(padOut[2], 0x00);
+        /* Restore a = 2 for subsequent tests */
+        ExpectIntEQ(BN_set_word(a, 2), 1);
+    }
+
     ExpectNotNull(str = BN_bn2hex(a));
     ExpectNotNull(BN_hex2bn(&b, str));
     ExpectIntEQ(BN_cmp(a, b), 0);

wolfssl/openssl/bn.h

@@ -135,6 +135,8 @@ WOLFSSL_API int wolfSSL_BN_cmp(const WOLFSSL_BIGNUM* a, const WOLFSSL_BIGNUM* b)
 WOLFSSL_API int wolfSSL_BN_ucmp(const WOLFSSL_BIGNUM* a, const WOLFSSL_BIGNUM* b);
 
 WOLFSSL_API int wolfSSL_BN_bn2bin(const WOLFSSL_BIGNUM* bn, unsigned char* r);
+WOLFSSL_API int wolfSSL_BN_bn2binpad(const WOLFSSL_BIGNUM* bn, unsigned char* r,
+                                     int tolen);
 WOLFSSL_API WOLFSSL_BIGNUM* wolfSSL_BN_bin2bn(const unsigned char* str, int len,
                                               WOLFSSL_BIGNUM* ret);
 
@@ -246,8 +248,9 @@ typedef WOLFSSL_BN_GENCB    BN_GENCB;
 #define BN_cmp    wolfSSL_BN_cmp
 #define BN_ucmp    wolfSSL_BN_ucmp
 
-#define BN_bn2bin  wolfSSL_BN_bn2bin
-#define BN_bin2bn  wolfSSL_BN_bin2bn
+#define BN_bn2bin     wolfSSL_BN_bn2bin
+#define BN_bn2binpad  wolfSSL_BN_bn2binpad
+#define BN_bin2bn     wolfSSL_BN_bin2bn
 
 #define BN_mod       wolfSSL_BN_mod
 #define BN_mod_exp   wolfSSL_BN_mod_exp