update examples: add rsa signature example

_examples/rsa_digital_signature.md

@@ -0,0 +1,57 @@
+### RSA Digital Signature PSS padding example
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "crypsi.h"
+
+char* load_file(char const* path);
+
+int main(int argc, char** argv) {
+    printf("hello\n");
+
+    char* message = "wuriyanto87e7d";
+
+    // load private key
+    unsigned char* rsa_private_key_char = load_file("private_key.txt");
+
+    unsigned int dst_signature_len;
+    unsigned char* dst_signature;
+
+    // Determine the size of the output
+    if (crypsi_rsa_sign_pss_sha256(rsa_private_key_char, message, strlen(message), &dst_signature, &dst_signature_len) != 0) {
+        printf("crypsi_rsa_sign_pss_sha256 failed\n");
+        exit(1);
+    }
+
+    printf("rsa signature result: %s\n", dst_signature);
+
+
+    free((void*) rsa_private_key_char);
+
+    return 0;
+}
+
+char* load_file(char const* path)
+{
+    char* buffer = 0;
+    long length;
+    FILE * f = fopen (path, "rb");
+
+    if (f != NULL) {
+      fseek (f, 0, SEEK_END);
+      length = ftell (f);
+      fseek (f, 0, SEEK_SET);
+      buffer = (char*) malloc((length+1)*sizeof(char));
+      if (buffer) {
+        fread(buffer, sizeof(char), length, f);
+      }
+
+      fclose(f);
+    }
+    buffer[length] = 0x0;
+
+    return buffer;
+}
+```

_examples/rsa_digital_signature_verify.md

@@ -0,0 +1,49 @@
+### RSA Verify Digital Signature PSS padding example
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "crypsi.h"
+
+char* load_file(char const* path);
+
+int main(int argc, char** argv) {
+    printf("hello\n");
+
+    char* signature = "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";
+    char* message = "wuriyanto";
+
+    unsigned char* rsa_public_key_char = load_file("public_key.txt");
+
+    int verify_result = crypsi_rsa_verify_sign_pss_sha256(rsa_public_key_char, message, strlen(message), signature, strlen(signature));
+
+    printf("rsa verify result: %d\n", verify_result);
+
+    free((void*) rsa_public_key_char);
+
+    return 0;
+}
+
+char* load_file(char const* path)
+{
+    char* buffer = 0;
+    long length;
+    FILE * f = fopen (path, "rb");
+
+    if (f != NULL) {
+      fseek (f, 0, SEEK_END);
+      length = ftell (f);
+      fseek (f, 0, SEEK_SET);
+      buffer = (char*) malloc((length+1)*sizeof(char));
+      if (buffer) {
+        fread(buffer, sizeof(char), length, f);
+      }
+
+      fclose(f);
+    }
+    buffer[length] = 0x0;
+
+    return buffer;
+}
+```