set6: challenge44: completed

1 files changed, 93 insertions, 0 deletions

diff --git a/set6/task44.c b/set6/task44.c
new file mode 100644
index 0000000..ffd92f3
--- /dev/null
+++ b/set6/task44.c
@@ -0,0 +1,93 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include "../lib/lib6.h"
+#include <openssl/sha.h>
+
+int main()
+{
+	int i;
+	struct dsa_public_params dsa_pub;
+	struct dsa_per_user_param dsa_user;
+	SHA_CTX sha1;
+
+	BIGNUM *mess1_hash_bn = BN_new();
+	BIGNUM *mess2_hash_bn = BN_new();
+	BIGNUM *s1_bn = BN_new();
+	BIGNUM *s2_bn = BN_new();
+
+	dsa_user.public = BN_new();
+	dsa_user.private = BN_new();
+	dsa_user.r = BN_new();
+	dsa_user.s = BN_new();
+
+	char *y = "2d026f4bf30195ede3a088da85e398ef869611d0f68f07"
+	"13d51c9c1a3a26c95105d915e2d8cdf26d056b86b8a7b8"
+	"5519b1c23cc3ecdc6062650462e3063bd179c2a6581519"
+	"f674a61f1d89a1fff27171ebc1b93d4dc57bceb7ae2430"
+	"f98a6a4d83d8279ee65d71c1203d2c96d65ebbf7cce9d3"
+	"2971c3de5084cce04a2e147821";
+
+	out = BIO_new(BIO_s_file());
+	BIO_set_fp(out, stdout, BIO_NOCLOSE);
+	ctx = BN_CTX_new();
+
+	init_dsa_pub_param(&dsa_pub);
+
+
+	// from the 44.txt the first message and the third last have
+	// the same r, which means the same k was used
+	char *r = "1105520928110492191417703162650245113664610474875";
+	char *s1 = "1267396447369736888040262262183731677867615804316";
+	char *s2 = "1021643638653719618255840562522049391608552714967";
+	char *mess1 = "Listen for me, you better listen for me now. ";
+	char *mess2 = "Pure black people mon is all I mon know. ";
+	char hash[20];
+	char hex[41];
+	
+	// save the public key
+	BN_hex2bn(&dsa_user.public, y);
+	BN_dec2bn(&s1_bn, s1);
+	BN_dec2bn(&s2_bn, s2);
+	BN_dec2bn(&dsa_user.s, s1);
+	BN_dec2bn(&dsa_user.r, r);
+
+	// computing SHA1 hashes for both messages
+	SHA1_Init(&sha1);
+	SHA1_Update(&sha1, mess1, strlen(mess1));
+	SHA1_Final(hash, &sha1);
+	BN_bin2bn(hash, 20, mess1_hash_bn);
+	hex_binary_to_string(hash, hex, 20);
+	printf("sha1 from mess1 is: %s\n", hex);
+
+	SHA1_Init(&sha1);
+	SHA1_Update(&sha1, mess2, strlen(mess2));
+	SHA1_Final(hash, &sha1);
+	BN_bin2bn(hash, 20, mess2_hash_bn);
+
+	BIGNUM *k = BN_new();
+	dsa_recover_k_from_repeated_nonce(mess1_hash_bn, mess2_hash_bn, s1_bn, s2_bn, &dsa_pub, &dsa_user, k);
+	dsa_recover_x_from_known_k(&dsa_pub, k, &dsa_user, mess1_hash_bn);
+	printf("\nreceovered x is:\n");
+	BN_print(out, dsa_user.private);
+	printf("\n");
+	// so dsa_user now contains the recovered private and public key,
+	// we can use to sign every new message
+
+	// compare hash of compute private key with given one
+	char *priv_key_bin = malloc(BN_num_bytes(dsa_user.private));
+	char *priv_key_hex = malloc(BN_num_bytes(dsa_user.private)*2+1);
+	BN_bn2bin(dsa_user.private, priv_key_bin);
+	hex_binary_to_string(priv_key_bin, priv_key_hex, BN_num_bytes(dsa_user.private));
+
+	SHA1_Init(&sha1);
+	SHA1_Update(&sha1, priv_key_hex, BN_num_bytes(dsa_user.private)*2);
+	SHA1_Final(hash, &sha1);
+	hex_binary_to_string(hash, hex, 20);
+	char *given_hash = "ca8f6f7c66fa362d40760d135b763eb8527d3d52";
+	printf("hash of recovered private key is: %s\n", hex);
+	printf("given hash is: %s\n", given_hash);
+	printf("equal ? : %i\n", memcmp(hex, given_hash, strlen(given_hash)));
+}