RSA PSS Example

.gitignore

@@ -145,3 +145,6 @@ pkcs11/server-tls-pkcs11
 pkcs11/softhsm2.conf
 pkcs11/softhsm2
 
+crypto/rsa-pss/rsa-pss
+crypto/rsa-pss/rsa-public.key
+crypto/rsa-pss/sign.txt

crypto/rsa-pss/Makefile

@@ -0,0 +1,11 @@
+CC=gcc
+CFLAGS=-Wall
+LIBS= -lwolfssl
+
+rsa-pss: rsa-pss.o
+	$(CC) -o $@ $^ $(CFLAGS) $(LIBS) 
+
+.PHONY: clean
+
+clean:
+	rm -f *.o rsa-pss

crypto/rsa-pss/README.md

@@ -0,0 +1,23 @@
+# RSA PSS Example
+
+## Building
+
+### Build wolfSSL
+
+```
+./configure --enable-rsapss --enable-keygen --enable-certgen --enable-certext
+make
+sudo make install
+```
+
+### Build rsa-pss
+`make`
+
+
+## Usage
+
+Creates a key-pair, exports public key to rsa-public.key and signs message in variable `szMessage`. 
+`./rsa-pss -o sign.txt`
+
+Uses public key at `rsa-public.key` to verify signed data.
+`./rsa-pss -v sign.txt`

crypto/rsa-pss/rsa-pss.c

@@ -0,0 +1,152 @@
+/* rsa-pss.c
+ *
+ * Copyright (C) 2006-2018 wolfSSL Inc.
+ *
+ * This file is part of wolfSSL.
+ *
+ * wolfSSL is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * wolfSSL is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335, USA
+ */
+
+/*
+* An implementation of RSA PSS digital signature using wolfSSL
+*/
+
+#include <stdio.h>
+#include <string.h>
+
+#include <wolfssl/options.h>
+#include <wolfssl/wolfcrypt/settings.h>
+#include <wolfssl/ssl.h>
+#include <wolfssl/wolfcrypt/rsa.h>
+
+static const char* kRsaPubKey = "./rsa-public.key";
+#define MAX_DER_SIZE 2048
+#define RSA_KEY_SIZE 2048
+
+int main(int argc, char** argv)
+{
+    RsaKey* pRsaKey = NULL;
+    WC_RNG rng;
+    const char* szMessage = "This is the string to be signed";
+    unsigned char pSignature[RSA_KEY_SIZE/8];
+    unsigned char pDecrypted[RSA_KEY_SIZE/8];
+    int status = 0;
+    int sz;
+    word32 idx = 0;
+    unsigned char derBuf[MAX_DER_SIZE];
+
+    pRsaKey = malloc(sizeof(RsaKey));
+    wolfSSL_Debugging_ON();
+
+    wolfSSL_Init();
+
+    wc_InitRsaKey(pRsaKey, NULL);
+    wc_InitRng(&rng);
+    wc_RsaSetRNG(pRsaKey, &rng);
+
+    if (memcmp(argv[1], "-o", 2) == 0) {
+        printf("generating RSA key to make a PSS signature\n");
+        /* Generate an RSA key pair */
+        if (wc_MakeRsaKey(pRsaKey, RSA_KEY_SIZE, 0x010001, &rng) != 0) {
+            printf("failed to create rsa key\n");
+        }
+
+        if (pRsaKey)
+        {
+            FILE* f;
+            f = fopen(kRsaPubKey, "wb");
+            printf("writing public key to %s\n", kRsaPubKey);
+            if (f == NULL) {
+                printf("unable to write out private key\n");
+            }
+            else {
+                sz = wc_RsaKeyToDer(pRsaKey, derBuf, sizeof(derBuf));
+                if (sz <= 0) {
+                    printf("error with rsa load der %d\n", sz);
+                }
+                fwrite(derBuf, 1, sz, f);
+                fclose(f);
+            }
+        }
+    }
+    else {
+        printf("reading in RSA key to verify signature\n");
+        sz = wolfSSL_PemPubKeyToDer(kRsaPubKey, derBuf, sizeof(derBuf));
+        wc_RsaPublicKeyDecode(derBuf, &idx, pRsaKey, sz);
+    }
+    if (!pRsaKey)
+    {
+        printf("RSA_generate_key failed with error\n");
+        goto prog_end;
+    }
+
+    if (memcmp(argv[1], "-o", 2) == 0) {
+        FILE* f = fopen(argv[2], "wb");
+        printf("Creating PSS signature and writing to %s\n", argv[2]);
+        if (f == NULL) {
+            printf("error opening output file %s\n", argv[2]);
+            goto prog_end;
+        }
+
+        /* perform digital signature */
+        status = wc_RsaPSS_Sign((byte*)szMessage, sizeof(szMessage),
+                pSignature, sizeof(pSignature),
+                WC_HASH_TYPE_SHA256, WC_MGF1SHA256, pRsaKey, &rng);
+        if (status <= 0)
+        {
+            printf("RSA_private_encrypt failed with error %d\n", status);
+            goto prog_end;
+        }
+
+        fwrite(pSignature, 1, status, f);
+        fclose(f);
+    }
+    else {
+        FILE* f;
+        f = fopen(argv[2], "rb");
+        if (f == NULL) {
+            printf("unable to open %s\n", argv[2]);
+            goto prog_end;
+        }
+        fread(pSignature, 1, sizeof(pSignature), f);
+        fclose(f);
+
+        /* now we will verify the signature
+        Start by a RAW decrypt of the signature
+        */
+        byte* pt = pDecrypted;
+        status = wc_RsaPSS_VerifyInline(pSignature, sizeof(pSignature), &pt,
+                WC_HASH_TYPE_SHA256, WC_MGF1SHA256, pRsaKey);
+        if (status <= 0)
+        {
+            printf("RSA_public_decrypt failed with error %d\n", status);
+            goto prog_end;
+        }
+        else
+        {
+            printf("RSA PSS verify success\n");
+        }
+   }
+
+prog_end:
+
+   if (pRsaKey)
+       free(pRsaKey);
+
+   wolfSSL_Cleanup();
+
+   return 0;
+}
+