While practicing, it is important to ensure that there are no weak keys.

Another needed attribute is that the key space designed to be flat, having no or very few weak keys.

A cipher with no weak keys is said to have a flat, or linear, key space.

Nevertheless, it is considered desirable for a cipher to have no weak keys.

The two main countermeasures against inadvertently using a weak key:

Some machines have more problems with weak keys than others, as modern block and stream ciphers do.

There are also 48 possibly weak keys that produce only four distinct subkeys (instead of 16).

Blowfish is known to be susceptible to attacks on reflectively weak keys.

Moreover, he also found a class of weak keys that can be detected and broken by the same attack with only 2 known plaintexts.

An algorithm that has unknown weak keys does not inspire much trust .

The military Enigma cipher machine, in its 3 and 4 rotor implementations had the equivalent of weak keys.

IDEA's weak keys are identifiable in a chosen-plaintext attack.

A simple study demonstrated the widespread use of weak keys by finding many embedded systems such as routers using the same keys.

These weak keys allow a cryptanalysis faster than exhaustive search using only 71 known plaintexts, for up to 11.5 rounds of Ake98.

DES also has four so-called weak keys.

DigiCert Malaysia has issued certificates with weak keys that it is unable to revoke.

Key stretching - A method to create a stronger key from a weak key or a weak shared secret.

Virtually all rotor based cipher machines (from 1925 onwards) have implementation flaws that lead to a substantial number of weak keys being created.

DES weak keys produce sixteen identical subkeys.

As in the case of DES, sometimes a small number of weak keys is acceptable, provided that they are all identified or identifiable.

Bhd, a Malaysian-based certification authority that issues certificates with weak keys and had its trust revoked by web browsers.

The key schedule is a simple linear feedback shift register, which updates every three rounds, resulting in some weak keys (e.g., the zero key).

More devastating attacks take advantage of certain weak keys in RC4 and eventually allow the WEP key itself to be recovered.

This variant allows for more choice in the cipher's parameters, and uses a modified key schedule to eliminate certain weak keys discovered by Don Coppersmith.

In cryptography, a weak key is a key, which, used with a specific cipher, makes the cipher behave in some undesirable way.