set5: task33

1 files changed, 62 insertions, 0 deletions

diff --git a/set5/task33.c b/set5/task33.c
new file mode 100644
index 0000000..9fbdcdd
--- /dev/null
+++ b/set5/task33.c
@@ -0,0 +1,62 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include <time.h>
+
+
+int DH_smallnums()
+{
+	srand(time(NULL));
+	// public prime numbers; everbody can know them, parameters of the
+	// expoential function
+	unsigned int p = 37;
+	unsigned int g = 5;
+	// exponents of the dicrect exponential function, should be kept secret
+	unsigned int b;
+	unsigned int a;
+	generate_random_bytes((char *)&a,4);
+	a = a % p;
+	generate_random_bytes((char *)&b,4);
+	b = b % p;
+	// A and B are the public keys, sent to each other
+	// one cannot infer a/b from A/B
+	unsigned A = g ^ a % p;
+	unsigned B = g ^ b % p;
+	// both compute these number, s1 = s2; (g^a)^b = (g^b)^a
+	unsigned int s1 = B ^ a % p;
+	unsigned int s2 = A ^ b % p;
+
+	printf("session key A: %i\n", s1);
+	printf("session key B: %i\n", s2);
+
+	// generate a key, 128 bit by hashing the session key
+}
+
+void DH_bignums()
+{
+	struct dh_param_bignum dh;
+
+	do_dh_key_exchange_bignum(&dh);
+
+	printf("bignums: A: ");
+	BN_print(out, dh.A);
+	printf("\nbignums: session key 1: ");
+	BN_print(out, dh.s1);
+	printf("\nbignums: session key 2: ");
+	BN_print(out, dh.s2);
+
+	if(BN_cmp(dh.s1, dh.s2) == 0)
+		printf("\nboth session keys are equal!\n");
+}
+
+int main()
+{
+	out = BIO_new(BIO_s_file());
+	BIO_set_fp(out, stdout, BIO_NOCLOSE);
+
+	ctx = BN_CTX_new();
+	DH_smallnums();
+	DH_bignums();
+}