Q

Plaintext space and key filling for RC4

What is the RC4 (128 bits) algorithm's plaintext space? Also, what is the key filling for the RC4 algorithm? Thank

you!

The machine that makes up the PRNG of the RC4 cipher has (256!) * (256^2) total states, which is about 2^1,700. Consequently, it's suitable for enciphering any reasonable quantity of data.

Nominally, RC4 accepts a key size of up to 2,048 bits. However, as noted above, there are only 1,700 bits worth of total states in the machine. Recently, cryptanalysis of the cipher has shown that it can (in theory) be broken with a work factor of around 600 bits. Thus, it's quite reasonable to use with 128-bit keys.


For more information on this topic, visit these other SearchSecurity.com resources:
  • Ask the Expert: What is RC4?
  • Ask the Expert: MD5 versus RC4 with 128-bit encryption
  • Best Web Links: Encryption
  • This was first published in April 2003

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