AES-128 keys unique for fixed plaintext/ciphertext pair?

[Sidney Markowitz]

Ed Gerck <egerck at nma.com> wrote:
 > For each AES-128 plaintext/ciphertext (c,p) pair with length
> equal to or larger than the unicity distance, there exists exactly
> one key k such that c=AES-128-Encrypt(p, k).

Excuse my naivete in the math for this, but is it relevant that the unicity
distance of ASCII text encrypted with a 128 bit key is about 150 bits
[Schneier, p 236] and the AES block size is only 128 bits? If you use plain
ECB mode is the plaintext/ciphertext length in the above statement 128 bits,
or does the statement imply that you have an arbitrary length (c,p) pair
using whatever mode, possibly chaining, makes sense for your purpose?

 -- sidney



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