PKCS Pad: public API to do PKCS padding

PKCS padding adds length of padding as repeated padding byte.
Use the new function in all places.

wolfcrypt/src/asn.c

@@ -9210,26 +9210,6 @@ int ToTraditionalEnc(byte* input, word32 sz, const char* password,
 
 #ifdef HAVE_PKCS12
 
-#define PKCS8_MIN_BLOCK_SIZE 8
-static int Pkcs8Pad(byte* buf, int sz, int blockSz)
-{
-    int padSz;
-
-    /* calculate pad size */
-    padSz = blockSz - (sz & (blockSz - 1));
-
-    /* pad with padSz value */
-    if (buf) {
-        int i;
-        for (i = 0; i < padSz; i++) {
-            buf[sz+i] = (byte)(padSz & 0xFF);
-        }
-    }
-
-    /* return adjusted length */
-    return sz + padSz;
-}
-
 #ifdef WOLFSSL_ASN_TEMPLATE
 /* ASN.1 template for PKCS #8 encrypted key with PBES1 parameters.
  * PKCS #8: RFC 5958, 3 - EncryptedPrivateKeyInfo
@@ -9339,7 +9319,7 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
 
     /* calculate size */
     /* size of constructed string at end */
-    sz = (word32)Pkcs8Pad(NULL, (int)inputSz, blockSz);
+    sz = wc_PkcsPad(NULL, inputSz, (word32)blockSz);
     totalSz  = ASN_TAG_SZ;
     totalSz += SetLength(sz, seq);
     totalSz += sz;
@@ -9435,7 +9415,7 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
     out[inOutIdx++] = ASN_CONTEXT_SPECIFIC | 0;
 
     /* get pad size and verify buffer room */
-    sz = (word32)Pkcs8Pad(NULL, (int)inputSz, blockSz);
+    sz = wc_PkcsPad(NULL, inputSz, (word32)blockSz);
     if (sz + inOutIdx > *outSz) {
     #ifdef WOLFSSL_SMALL_STACK
         XFREE(saltTmp, heap, DYNAMIC_TYPE_TMP_BUFFER);
@@ -9446,7 +9426,7 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
 
     /* copy input to output buffer and pad end */
     XMEMCPY(out + inOutIdx, input, inputSz);
-    sz = (word32)Pkcs8Pad(out + inOutIdx, (int)inputSz, blockSz);
+    sz = wc_PkcsPad(out + inOutIdx, inputSz, (word32)blockSz);
 #ifdef WOLFSSL_SMALL_STACK
     cbcIv = (byte*)XMALLOC(MAX_IV_SIZE, heap, DYNAMIC_TYPE_TMP_BUFFER);
     if (cbcIv == NULL) {
@@ -9520,7 +9500,7 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
                 salt, saltSz);
         SetASN_Int16Bit(&dataASN[P8ENCPBES1ASN_IDX_ENCALGO_PBEPARAM_ITER],
                         (word16)itt);
-        pkcs8Sz = (word32)Pkcs8Pad(NULL, (int)inputSz, blockSz);
+        pkcs8Sz = wc_PkcsPad(NULL, inputSz, (word32)blockSz);
         SetASN_Buffer(&dataASN[P8ENCPBES1ASN_IDX_ENCDATA], NULL, pkcs8Sz);
 
         /* Calculate size of encoding. */
@@ -9558,7 +9538,7 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
         byte* pkcs8 =
             (byte*)dataASN[P8ENCPBES1ASN_IDX_ENCDATA].data.buffer.data;
         XMEMCPY(pkcs8, input, inputSz);
-        Pkcs8Pad(pkcs8, (int)inputSz, blockSz);
+        (void)wc_PkcsPad(pkcs8, inputSz, (word32)blockSz);
 
         /* Encrypt PKCS#8 key inline. */
         ret = wc_CryptKey(password, passwordSz, salt, (int)saltSz, itt, id,
@@ -9578,6 +9558,36 @@ int EncryptContent(byte* input, word32 inputSz, byte* out, word32* outSz,
 #endif /* HAVE_PKCS12 */
 #endif /* NO_PWDBASED */
 
+/* Block padding used for PKCS#5, PKCS#7, PKCS#8 and PKCS#12.
+ *
+ * The length of padding is the value of each padding byte.
+ *
+ * When buf is NULL, the padded size is returned.
+ *
+ * @param [in, out] buf      Buffer of data to be padded. May be NULL.
+ * @param [in]      sz       Size of data in bytes.
+ * @param [in]      blockSz  Size of block, in bytes, which buffer size must be
+ *                           a multiple of. Assumed to be less than 256 and
+ *                           a power of 2.
+ * @return  Size of padded buffer in bytes.
+ */
+word32 wc_PkcsPad(byte* buf, word32 sz, word32 blockSz)
+{
+    /* Calculate number of padding bytes. */
+    word32 padSz = blockSz - (sz & (blockSz - 1));
+
+    /* Pad with padSz byte. */
+    if (buf != NULL) {
+        word32 i;
+        for (i = 0; i < padSz; i++) {
+            buf[sz+i] = (byte)(padSz & 0xFF);
+        }
+    }
+
+    /* Return padded buffer size in bytes. */
+    return sz + padSz;
+}
+
 #ifndef NO_RSA
 #ifdef WOLFSSL_ASN_TEMPLATE
 /* ASN.1 template for an RSA public key.

wolfcrypt/src/pkcs7.c

@@ -8706,14 +8706,10 @@ int wc_PKCS7_SetContentType(wc_PKCS7* pkcs7, byte* contentType, word32 sz)
 /* return size of padded data, padded to blockSz chunks, or negative on error */
 int wc_PKCS7_GetPadSize(word32 inputSz, word32 blockSz)
 {
-    word32 padSz;
-
     if (blockSz == 0)
         return BAD_FUNC_ARG;
 
-    padSz = blockSz - (inputSz % blockSz);
+    return (int)(blockSz - (inputSz % blockSz));
-
-    return (int)padSz;
 }
 
 
@@ -8722,28 +8718,16 @@ int wc_PKCS7_GetPadSize(word32 inputSz, word32 blockSz)
 int wc_PKCS7_PadData(byte* in, word32 inSz, byte* out, word32 outSz,
                      word32 blockSz)
 {
-    int ret;
-    word32 i, padSz;
-
     if (in == NULL  || inSz == 0 ||
-        out == NULL || outSz == 0)
+        out == NULL || outSz == 0 || blockSz == 0)
         return BAD_FUNC_ARG;
 
-    ret = wc_PKCS7_GetPadSize(inSz, blockSz);
+    if (outSz < wc_PkcsPad(NULL, inSz, blockSz))
-    if (ret < 0)
-        return ret;
-    padSz = (word32)ret;
-
-    if (outSz < (inSz + padSz))
         return BAD_FUNC_ARG;
 
     XMEMCPY(out, in, inSz);
 
-    for (i = 0; i < padSz; i++) {
+    return (int)wc_PkcsPad(out, inSz, blockSz);
-        out[inSz + i] = (byte)padSz;
-    }
-
-    return (int)(inSz + padSz);
 }
 
 

wolfcrypt/test/test.c

@@ -3065,6 +3065,9 @@ WOLFSSL_TEST_SUBROUTINE wc_test_ret_t asn_test(void)
     struct tm timearg;
     time_t now;
 #endif
+    int i;
+    unsigned char buf[16];
+
     WOLFSSL_ENTER("asn_test");
 
     ret = wc_GetDateInfo(dateBuf, (int)sizeof(dateBuf), &datePart, &format,
@@ -3093,6 +3096,31 @@ WOLFSSL_TEST_SUBROUTINE wc_test_ret_t asn_test(void)
         return WC_TEST_RET_ENC_EC(ret);
 #endif /* !NO_ASN_TIME */
 
+    /* Test that only calculating the length works. */
+    for (i = 16; i < 32; i++) {
+        ret = wc_PkcsPad(NULL, i, 16);
+        if (ret != i + (16 - (i % 16)))
+            return WC_TEST_RET_ENC_I(i);
+    }
+
+    /* Test that adding padding works. */
+    XMEMSET(buf, 0xa5, sizeof(buf));
+    for (i = 15; i >= 0; i--) {
+        int j;
+        ret = wc_PkcsPad(buf, i, 16);
+        if (ret != 16)
+            return WC_TEST_RET_ENC_I(i);
+        /* Check padded buffer. */
+        for (j = 0; j < 16; j++) {
+            /* Check buffer bytes haven't been modified. */
+            if ((j < i) && (buf[j] != 0xa5))
+                return WC_TEST_RET_ENC_I(i);
+            /* Check padding bytes are correct. */
+            if (j >= i && (buf[j] != (16 - i)))
+                return WC_TEST_RET_ENC_I(i);
+        }
+    }
+
     return 0;
 }
 #endif /* !NO_ASN */

wolfssl/wolfcrypt/asn_public.h

@@ -729,6 +729,8 @@ WOLFSSL_API void wc_FreeDer(DerBuffer** pDer);
                                 word32 outputSz, byte *cipherIno, int type);
 #endif
 
+WOLFSSL_API word32 wc_PkcsPad(byte* buf, word32 sz, word32 blockSz);
+
 #ifndef NO_RSA
     WOLFSSL_API int wc_RsaPublicKeyDecode_ex(const byte* input, word32* inOutIdx,
         word32 inSz, const byte** n, word32* nSz, const byte** e, word32* eSz);