Creating apps/, for small utilities.

* Naming a new directory holding small utilities/scripts to be used whenever
  testing the application.
* Adding a small program gen.c, which generates a standard pem file, given as
  input the pair of primes {p, q} and the two exponents {d, e}.

src/apps/gen.c

@@ -0,0 +1,65 @@
+/**
+ * \file gen.c
+ *
+ * Generate a fake RSA certificate file, given as input e, d, p, q.
+ */
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <openssl/bn.h>
+#include <openssl/ssl.h>
+#include <openssl/rsa.h>
+
+
+void usage(void)
+{
+  static const char* help_message = "%s usage: %s"
+    " <pub key> <priv key> <p> <q>"
+    "\n";
+  fprintf(stderr, help_message, program_invocation_short_name,
+          program_invocation_name);
+}
+
+int main(int argc, char **argv)
+{
+  BN_CTX* ctx;
+  BIGNUM* p1, *q1;
+  RSA* rsa;
+
+  rsa = RSA_new();
+  p1 = BN_new();
+  q1 = BN_new();
+  ctx = BN_CTX_new();
+  rsa->n = BN_new();
+  rsa->iqmp = BN_new();
+  rsa->dmp1 = BN_new();
+  rsa->dmq1 = BN_new();
+
+  if (argc < 4+1) {
+    usage();
+    return EXIT_FAILURE;
+  }
+
+  BN_dec2bn(&rsa->e, argv[1]);
+  BN_dec2bn(&rsa->d, argv[2]);
+  BN_dec2bn(&rsa->p, argv[3]);
+  BN_dec2bn(&rsa->q, argv[4]);
+  BN_mul(rsa->n, rsa->p, rsa->q, ctx);
+  BN_sub(p1, rsa->p, BN_value_one());
+  BN_sub(q1, rsa->q, BN_value_one());
+  BN_mod(rsa->dmq1, rsa->d, q1, ctx);
+  BN_mod(rsa->dmp1, rsa->d, p1, ctx);
+  BN_mod_inverse(rsa->iqmp, rsa->q, rsa->p, ctx);
+  PEM_write_RSAPrivateKey(stdout, rsa, NULL, NULL, 0, NULL, NULL);
+
+
+  BN_CTX_free(ctx);
+  BN_free(q1);
+  BN_free(p1);
+  RSA_free(rsa);
+
+  return 0;
+}