AES_128_CBC_RK (community library)

Summary

Implementation of AES 128 CBC hash algorithm for Particle devices

Example Build Testing

Library Read Me

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AES 128 CBC Library

Implementation of AES 128 (CBC mode) for Particle Devices

API

AES_ctx

struct AES_ctx
{
uint8_t RoundKey[AES_keyExpSize];
uint8_t Iv[AES_BLOCKLEN];
};

The AES_ctx structure holds the encryption/decryption context for a session. It's 192 bytes for AES 128.

• AES_keyExpSize = 176
• AES_BLOCKLEN = 16

AES_init_ctx_iv

void AES_init_ctx_iv(struct AES_ctx* ctx, const uint8_t* key, const uint8_t* iv);
void AES_init_ctx(struct AES_ctx* ctx, const uint8_t* key);
void AES_ctx_set_iv(struct AES_ctx* ctx, const uint8_t* iv);

You typically initialize it using AES_init_ctx_iv. The parameters are:

• key (const uint8_t *) The secret private shared key between the sender and receiver. It's always 16 bytes long.
• iv (const uint8_t *) The initialization vector is a 16-byte random value. It assures that the given the same plaintext and key, the encrypted output is not the same. The iv should be randomly generated and does not need to be kept secret. You can transmit the iv in clear text, which is a common scenario because the other side cannot decrypt without the iv.

There are also functions to set the key and iv separately.

AES_CBC_encrypt_buffer

void AES_CBC_encrypt_buffer(struct AES_ctx* ctx, uint8_t* buf, uint32_t length);

Encrypt a block of data. length must be a multiple of AES_BLOCKLEN bytes (16). Encryption is done in place, overwriting the plain text.

AES_CBC_decrypt_buffer

void AES_CBC_decrypt_buffer(struct AES_ctx* ctx, uint8_t* buf, uint32_t length);

Decrypt a block of data. length must be a multiple of AES_BLOCKLEN bytes (16). Decryption is done in place, overwriting the cypher text.

Because of the fixed block size if you are encrypting arbitrary stream data you'll need an out-of-band method of determining how much actual data there is. The AES ECB mode supports arbitrary length and is suitable for streams, except it's also insecure and is not recommended for any use.

Original Library

https://github.com/kokke/tiny-AES-c

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Revision History

0.0.1 (2020-08-07)

• Initial version

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