fixed bug in valid_pkcs_padding

The input length shut be a multiple of the blocksize. However we checked
if the inpute length was a multiple of the number of padded bytes.

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/lib2.c b/lib/lib2.c
index 70a7160..c7e6ebb 100644
--- a/lib/lib2.c
+++ b/lib/lib2.c
@@ -41,7 +41,7 @@ int valid_pkcs7_padding(const char *in, int length_in, char *unpadded, int block
 	}
 	
 	padding_length = length_in - i;
-	if ((length_in % padding_length) != 0)
+	if ((length_in % blocksize) != 0)
 		return 0;
 
 	if(in[length_in-1] != padding_length)
@@ -385,7 +385,6 @@ int challenge16_encrypt(char *input, char **encrypted)
 	res[strlen(prepend)+strlen(input)+strlen(append)+2*quote_char+1] = '\0';	
 	// padding
 	unencrypted = pkcs7_padding(res, strlen(res), 16);
-	printf("%s\n", unencrypted);
 	*encrypted = malloc(strlen(unencrypted));
 	aes_cbc(unencrypted, strlen(unencrypted), *encrypted, key, iv , 1);
 	return strlen(unencrypted);
@@ -398,7 +397,11 @@ void challenge16_decrypt(char *encrypted, int length)
 	
 	aes_cbc(encrypted, length, unencrypted, key, iv, 0);
 	// unpadd
-	valid_pkcs7_padding(unencrypted, length, unpadd, 16);
+	int ret = valid_pkcs7_padding(unencrypted, length, unpadd, 16);
+	if(!ret) {
+		printf("no valid padding!\n");
+		return;
+	}
 	// look for string ;admin=true;
 	printf("unencrpyted string: %s\n", unpadd);
 }