Cryptography system that limits the length of the encypted message I have two devices which communicate via sms.

This communication should now be encrypted.

The devices can only send messages with the lenght of 160 characters.

So i am looking for an encryption system which can limit the length of the encypted message to 160.

Is there such a cryptography system?
Which system that meets this requirement is the safest?
As encryption scheme that could only encrypt fix length message is a important essence in cryptography, e.g. one-time pad.  Block cipher is a better example, e.g. AES is a popular block cipher whose block size is 128 bits.  While given such block cipher who could only encrypt 128-bit string, you can construct encryption scheme that encrypt arbitrary length string.  

The security of the encryption scheme is not determined by the length of message but by the length of the key.  For example, AES has variant using 128-bit, 192-bit, 256-bit key.  AES-256, who use 256-bit key, is considered to be safer.  

Finally, for ultimate security, you should use one-time pad.  One-time pad is information-theoretically secure which means the most powerful adversary can not break the cipher.  The disadvantage is the key could be only used once.  You could store multiple keys in your devices.  10MB space could store more than 60000 pre-shared keys, which sustain 60000 secure SMS message.