# Re: A cipher operates with more possible plaintexts than possible keys. What does this mean?

*From*: kg <kristiag+news@xxxxxxxxxxxx>*Date*: Sat, 12 Mar 2011 09:13:56 +0000 (UTC)

rossum <rossum48@xxxxxxxxxxxx> wrote:

On Tue, 08 Mar 2011 17:07:23 GMT, unruh

<unruh@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

Any cypher except theOTP has a smaller key than plaintexts. It meansNitpick: Any cypher except the OTP has a smaller key than _the largest

that it is theoretically breakable, if the plaintext has structure to

it.

possible_ plaintexts.

I may want to encipher "No" which is smaller than most keys. Even

with padding it will not be larger than most block cypher keys.

While we're picking nits: There are many ciphers with a key that's larger

than the largest possible plaintext.

Example: The alphabet is Zn, the key is a sequence of pairs (ai,bi),

such that ai is invertible in Zn, and we encrypt (x1,x2,...,xn) as

(a1*x1+b1, ..., an*xn+bn).

The key is much larger than the largest possible plaintext.

--

kg

.

**References**:**A cipher operates with more possible plaintexts than possible keys. What does this mean?***From:*ping pong

**Re: A cipher operates with more possible plaintexts than possible keys. What does this mean?***From:*unruh

**Re: A cipher operates with more possible plaintexts than possible keys. What does this mean?***From:*rossum

- Prev by Date:
**Re: DES - more simple idea seems the correct one** - Next by Date:
**Re: DES - more simple idea seems the correct one** - Previous by thread:
**Re: A cipher operates with more possible plaintexts than possible keys. What does this mean?** - Next by thread:
**Re: A cipher operates with more possible plaintexts than possible keys. What does this mean?** - Index(es):