How to use tiny-aes 128 library in c? - c

Question

I would like to encrypt using tiny AES library (https://github.com/kokke/tiny-AES-c) in C for AES128.
My code is as below:
unsigned char cipher[64];
unsigned char in[] = "THJmaoeuf2jsn4jebc7ak3mUdnyHeklOYopdna/OOndu3bis/E7jTd/enasduR3h"; //64 bits
printf("Size of AES input msg: %d \n", sizeof(in));
unsigned char key[] = "Gns7AauH3dnaod=="; //16 bits
unsigned char IV[] = "vhdNaleuTHenaOlL"; //16 bits
printf("cipher(before): %x \n", cipher);
AES128_CBC_encrypt_buffer(cipher, in, 64, key, IV);
for(int n=0; n<64; n++){
printf("cipher[%d]: %x \n", n, cipher);
}
The function I am using from tiny AES 128 library is this :
void AES128_CBC_encrypt_buffer(uint8_t* output, uint8_t* input, uint32_t length, const uint8_t* key, const uint8_t* iv)
However, the last line of printing 'cipher' is empty. I believe it should print the cipher text of the original input after encryption. Is this the correct way to use the library? Thank you.
EDIT: I updated the code here, in which 'cipher' is now printing characters but in a strange way. It prints the same thing before and after encryption, which should not be the case. This is the same case even when I changed the 'key' and 'IV' to be 16 bits and input message 'in' as 64 bits. Here is a part of the output:
cipher(before): 20003A34
cipher[0]: 20003A34
cipher[1]: 20003A34
cipher[2]: 20003A34
.
.
cipher[63]: 20003A34

Answer 1

Your code has undefined behavior.
This:
unsigned char *cipher = "";
makes cipher into a pointer to a single byte with the value 0 (the string terminator). It's a bit fishy since string literals are not guaranteed to be unsigned char (they're just char which is either signed or unsigned) but I think it will build.
This doesn't give you any writeable space, since string literals are read-only, so trying to write an entire encrypted block in there will give you undefined behavior.
To fix it you need:
unsigned char in[] = "THJmaoeuf2jsn4jebc7ak3mUdnyHeklOYopdna/OOndu3bis/E7jTd/enasduR3h"; //64 bits
unsigned char cipher[sizeof in];
Also, the encrypted data is very likely not a valid C string, it can contain 0-bytes and thus won't print correctly using printf("%s", ...); anyway.

Answer 2

in the line:
printf("cipher[%d]: %x \n", n, cipher);
change that to be:
printf("cipher[%d]: %x \n", n, cipher[n]);
That way, each byte of the cipher is outputted instead of the address of cipher which is what you are getting.

Answer 3

in aes.h select 128 by
#define AES128 1
and below is a sample for Encryption & Decryption
struct AES_ctx ctx;
uint8_t key[] = "aaaaaaaaaaaaaaaa";
uint8_t iv[] = "bbbbbbbbbbbbbbbb";
uint8_t str[] = "This a sample text, Length eq 32";
printf("\n raw buffer \n");
for (int i = 0; i < 32; ++i) {
printf("%.2x", str[i]);
}
AES_init_ctx_iv(&ctx, key, iv);
AES_CBC_encrypt_buffer(&ctx, str, 32);
printf("\n Encrypted buffer\n");
for (int i = 0; i < 32; ++i) {
printf("%.2x", str[i]);
}
printf("\n Decrypted buffer\n");
AES_init_ctx_iv(&ctx, key, iv);
AES_CBC_decrypt_buffer(&ctx, str, 32);
for (int i = 0; i < 32; ++i) {
printf("%.2x", str[i]);
}
printf("\n");
*Note: there is no padding is provided so for CBC and ECB, All buffers should be multiples of 16 bytes.