1 files changed, 70 insertions, 0 deletions
diff --git a/set6/task42.c b/set6/task42.c
new file mode 100644
index 0000000..253836c
--- /dev/null
+++ b/set6/task42.c
@@ -0,0 +1,70 @@
+#include "../lib/lib.h"
+#include "../lib/lib2.h"
+#include "../lib/lib3.h"
+#include "../lib/lib4.h"
+#include "../lib/lib5.h"
+#include "../lib/lib6.h"
+/**
+  * you do not have the secrect key to sign the message
+  * but you try to find a number which gives a "valid" padding
+  * if the number is e-th rooted
+  * to verfiy the signature the message is exponiated with e
+  * when this didn't wrap around then it is a "valid" padding
+  *
+  * make the littlest possible number and exponiated it with e
+  * hope that it did not wrap around and the e-th root is 
+  *
+  **/
+int main()
+{
+	struct rsa_key_bignum public, private;
+	SHA1Context sha1;
+
+	BIGNUM *mess = BN_new();
+	BIGNUM *forged = BN_new();
+	BIGNUM *signed_mess = BN_new();
+	BIGNUM *restored = BN_new();
+	out = BIO_new(BIO_s_file());
+	BIO_set_fp(out, stdout, BIO_NOCLOSE);
+
+	ctx = BN_CTX_new();
+
+	char *str_mess = "hi mom";
+	char *sha1_hash[20];
+	int pk_mess_len = 20 + strlen(str_mess) + 4 + 50;
+	char *pk_mes = malloc(pk_mess_len);
+	
+	rsa_generate_key_bignum(&public, &private);
+
+	SHA1Reset(&sha1);
+	SHA1Input(&sha1, str_mess, strlen(str_mess));
+	SHA1Result(&sha1);
+	memcpy(sha1_hash, &(sha1.Message_Digest), 20);
+
+	pk_mes[0] = 0x00;
+	pk_mes[1] = 0x01;
+	pk_mes[2] = 0xff;
+	pk_mes[3] = 0x00;
+	memcpy(&pk_mes[4], sha1_hash, 20);
+
+	// does this padding verify?
+	printf("padding verfied: %i\n", shitty_pkcs1_5_padding_verify(pk_mes, pk_mess_len, str_mess));
+	BN_bin2bn(pk_mes, pk_mess_len, mess);
+	// sign with knowing the private key
+	//rsa_encrypt_bignum(mess, signed_mess, &private);
+	// "sign" without knowing the private key
+	BIGNUM *n3 = BN_new();
+	BN_set_word(n3, 3);
+	nth_root_bignum(signed_mess, mess, n3);
+
+
+	// verfiy
+	rsa_decrypt_bignum(signed_mess, restored, &public);
+
+	char *rest_mess = malloc(BN_num_bytes(restored));
+	BN_bn2bin(restored, rest_mess);
+
+	printf("\nverfied after cube root and exp: %i\n", shitty_pkcs1_5_padding_verify(rest_mess, BN_num_bytes(restored), str_mess));
+	printf("padding from better verifier function: %i\n",
+		pkcs1_5_padding_verify(pk_mes, pk_mess_len, str_mess));
+}