OpenSSL EVP aes_256_cbc Initialization Vector Size

Question

I'm looking at the crypto library examples (programmed in c) provided for OpenSSL EVP on OpenSSL Wiki.

Their example for a 128 bit Initialization Vector is as follows:

/* A 128 bit IV */  
unsigned char *iv = (unsigned char *)"01234567890123456";

0-9 -> 10 chars
0-6 -> 7 chars
Total: 17 chars

Each char is 1 byte(8 bits) on my system. Hence the IV is 8*17 = 136 bits. Why are they saying that the total IV size is 128 bits? Is this an off-by-1 error or am I missing something?

Answer 1

Moved from the question to an answer.

Stephen was correct. This was very simple to check, I just changed the IV to be the correct length and the ciphertext remained the same. Hence, the extra byte is not used in the algorithm and somebody miscounted.

Default IV:

/* A 128 bit IV */  
unsigned char *iv = (unsigned char *)"01234567890123456";

Output:

Ciphertext is:  
0000 - e0 6f 63 a7 11 e8 b7 aa-9f 94 40 10 7d 46 80 a1   .oc.......@.}F..  
0010 - 17 99 43 80 ea 31 d2 a2-99 b9 53 02 d4 39 b9 70   ..C..1....S..9.p  
0020 - 2c 8e 65 a9 92 36 ec 92-07 04 91 5c f1 a9 8a 44   ,.e..6.....\...D  

New IV:

/* A 128 bit IV */  
unsigned char *iv = (unsigned char *)"0123456789012345";

Run make again to build the program.

Output:

Ciphertext is:  
0000 - e0 6f 63 a7 11 e8 b7 aa-9f 94 40 10 7d 46 80 a1   .oc.......@.}F..  
0010 - 17 99 43 80 ea 31 d2 a2-99 b9 53 02 d4 39 b9 70   ..C..1....S..9.p  
0020 - 2c 8e 65 a9 92 36 ec 92-07 04 91 5c f1 a9 8a 44   ,.e..6.....\...D