-12-
v7.0
Confidentiality (privacy)
•
CBC mode:
Each 16-byte block of plaintext is XORed with the previous ciphertext block before being encrypted. This
way, each ciphertext block depends on all plaintext blocks processed up to that point. To make each message unique, an
initialization vector
must be used in the first block. This initialization vector size is 16 bytes, so is the same size as the data
block size. Notice that this mode is not supported by Meshlium.
Figure : ECB mode encryption
A block cipher works on fixed size blocks, but messages come in a variety of lengths. So some modes of operation require that
the final block be padded before encryption. Several padding schemes exist, but this library provide two padding schemes:
•
ZEROS
: this method adds 0s until the last block size is completed. Notice that this mode is the only one supported by
Meshlium.
•
PKCS5
: this method adds the input at the trailing end with k - (l mod k) octets all having value k - (l mod k), where l is the
length of the input. Notice that this mode is not supported by Meshlium.
AES Algorithm
Key Size
Data Block Size
AES-128
128 bits
16 bytes
AES-192
192 bits
16 bytes
AES-256
256 bits
16 bytes
