set6: challenge 46: completed

1 files changed, 79 insertions, 0 deletions

diff --git a/set6/task46.c b/set6/task46.c
new file mode 100644
index 0000000..069e858
--- /dev/null
+++ b/set6/task46.c
@@ -0,0 +1,79 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include "../lib/lib6.h"
+#include <openssl/sha.h>
+
+int main()
+{
+	struct rsa_key_bignum private, public;
+
+	out = BIO_new(BIO_s_file());
+	BIO_set_fp(out, stdout, BIO_NOCLOSE);
+	ctx = BN_CTX_new();
+
+	private.modulo = BN_new();
+	private.exponent = BN_new();
+	public.modulo = BN_new();
+	public.exponent = BN_new();
+
+
+	__rsa_generate_key_bignum(&public, &private, 512);
+
+	char *message_base64 = "VGhhdCdzIHdoeSBJIGZvdW5kIHlvdSBkb24ndCBwbGF5IG"
+		"Fyb3VuZCB3aXRoIHRoZSBGdW5reSBDb2xkIE1lZGluYQ==";
+
+	char *message = malloc(strlen(message_base64)*2);
+	int message_len = decode_base64(message_base64, message);
+
+	BIGNUM *message_bn = BN_new();
+	BIGNUM *encrypted = BN_new();
+	BIGNUM *decrypted = BN_new();
+	BN_bin2bn(message, message_len, message_bn);
+	// encrpyted message now
+	rsa_encrypt_bignum(message_bn, encrypted, &public);
+	printf("encrypted is\n");
+	BN_print(out, encrypted);
+
+	rsa_decrypt_bignum(encrypted, decrypted, &private);
+	printf("\ndecrypted:\n");
+	BN_print(out, decrypted);
+
+	// so all we want if finding a number between [0,N] which represents
+	// the plaintext.
+	// doing kind of binary search here, always split in half
+	int odd = 0;
+	BIGNUM *min = BN_new();
+	BIGNUM *max = BN_new();
+	BIGNUM *n2 = BN_new();
+	BIGNUM *ne2 = BN_new();
+	BIGNUM *tmp = BN_new();
+	BIGNUM *diff = BN_new();
+	BN_set_word(n2, 2);
+	BN_mod_exp(ne2, n2, public.exponent, public.modulo, ctx);
+	BN_copy(tmp, encrypted);
+	BN_zero(min);
+	BN_copy(max, public.modulo);
+
+	// when min and max are equal we found our plaintext
+	while(BN_cmp(min,max) != 1) {
+		BN_sub(diff, max, min);
+		if(BN_is_one(diff))
+			break;
+		BN_div(diff, NULL, diff, n2, ctx);
+		// multiply ciphertext with 2^e so that plaintext is multiplied
+		// by 2
+		BN_mod_mul(tmp, ne2, tmp, public.modulo, ctx);
+		odd = rsa_parity_orcale(tmp, &private);
+		if (!odd)
+			BN_sub(max, max, diff);
+		else
+			BN_add(min, min, diff);
+	}
+	printf("\ndecrypted plaintext is:\n");
+	BN_print(out, max);
+	char *readable_mess = malloc(BN_num_bytes(max));
+	BN_bn2bin(max, readable_mess);
+	printf("\nmessage is: %s\n", readable_mess);
+}