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Why is stream cipher not secure?

Stream ciphers are dangerous to use with stored data, or if the key is used more than once. Stream ciphers are vulnerable to “key re-use” attacks, also called “two-time pad” attacks. This is insecure as it would require re-using the same IV every time the stored data needs to be modified.

What happens if the keystream repeats?

The purpose of the IV is to allow reuse of the same key for several different messages, i.e., to avoid the keystream to be repeated. Each message is then associated with a new IV, which can be either computed using a counter or be arbitrarily chosen by the sender.

Can a stream cipher be perfectly secure?

A stream cipher is an encryption algorithm that encrypts 1 bit or byte of plaintext at a time. The key of a stream cipher is no longer as long as the original message. Hence, it can no longer guarantee “perfect secrecy”. However, it can still achieve a strong level of security.

Can stream cipher reuse keys?

Reused key attack. Stream ciphers are vulnerable to attack if the same key is used twice (depth of two) or more. Say we send messages A and B of the same length, both encrypted using same key, K. The stream cipher produces a string of bits C(K) the same length as the messages.

What drawbacks are stream ciphers trying to overcome?

Disadvantages: Slowness of encryption: an entire block must be accumulated before encryption / decryption can begin. Error propogation: An error in one symbol may corrupt the entire block. An encryption algorithm is said to be malleable if transformations on the ciphertext produce meaningful changes in the plaintext.

Is block or stream cipher better?

Stream algorithms are faster and more efficient than block ciphers because they’re encrypting only one bit of data at a time into individual symbols rather than entire blocks.

Is AES stream cipher?

AES-CTR is a stream cipher, of a particular kind where the keystream is obtained by encryption of a counter.

Is one-time pad a stream cipher?

Stream ciphers can encrypt plaintext messages of variable length. The one-time pad can be thought of as an example – each message uses a portion of the key with length equal to the length of the plaintext message.

Is Stream Cipher faster than block cipher?

Why is ECB not safe?

The main reason not to use ECB mode encryption is that it’s not semantically secure — that is, merely observing ECB-encrypted ciphertext can leak information about the plaintext (even beyond its length, which all encryption schemes accepting arbitrarily long plaintexts will leak to some extent).

What is IV in stream cipher?

In cryptography, an initialization vector (IV) is a block of bits that is required to allow a stream cipher or a block cipher to be executed in any of several modes of operation to produce a unique stream independent from other streams produced by the same encryption key, without having to go through a (usually lengthy …

Can you try every possible key on a piece of ciphertext?

Brute-force attack: The attacker tries every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained. On average, half of all possible keys must be tried to achieve success.