Input limitations on the RC6 cipher RSA has limitation in input size for encryption and decryption.


Can RC6 be used for encryption and decryption of files larger than 5 MB?
Is there any limitation for input size? 
Is RC6 safe for using encryption or has it faced any attacks?
RC6 is secure, and has no effective limit on input size.

RSA is an asymmetric cipher. It is not designed for general purpose encryption, and so has a very tight limit on the amount of data that can be encrypted. In fact, unlike symmetric ciphers, textbook RSA is based on a mathematical problem, so the ciphertext is the plaintext raised to an public exponent, modulo a large public integer. This modular operation puts a hard limit on the length of the plaintext to be encrypted. Note that RSA is not used to encrypt anything directly. It is used to encrypt a smaller symmetric key which is then used to protect the confidentiality of further communications.

RC6 is a symmetric block cipher. The amount of data that can be encrypted with a single key depends on the mode of operation in use, as well as the block size of the cipher. For a cipher with 128-bit blocks, like RC6, the amount of data it can securely encrypt is vast. To put it into hard numbers, in order to have an already astronomically small 2-32 chance of leaking a little bit of information from one 128-bit block in CBC mode, you need to encrypt more than four petabytes of data with one key. A mere five megabytes is nothing.

There are no known attacks which weaken RC6 to the point that breaking it is practical. As it did not win the AES competition however, it has received comparatively less analysis. A large amount of information on its security can be found by searching "rc6 cryptanalysis pdf".



Obligatory disclaimer: Choosing the cipher is the easiest part of implementing a secure cryptosystem. If you are designing your own cryptosystem, don't. Simply using RC6 is not enough to provide security. You need to choose the proper mode of operation, use authentication, use a secure KDF if the key is to be derived from a password, mitigate a variety of attacks if used on the network (reflection, replay, man-in-the-middle, etc). Don't think that, just because you are using a secure cipher, that the data you encrypt is secure.