Can you reuse keys for a stream cipher?

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 is the weakness about using the same key stream multiple times for encryption in a stream cipher?

Stream ciphers are vulnerable to “key re-use” attacks, also called “two-time pad” attacks. This type of vulnerability occurs when you use the same key more than once because it is trivial to XOR the two ciphertext strings and nullify the key, which leaves only XOR’ed plain text.

What are the pros and cons of stream ciphers?

Stream ciphers encrypt one bit or byte at a time while block ciphers work on chunks/blocks of data at a time.

• Stream ciphers are faster than block.
• Block ciphers typically require more memory.
• Stream ciphers are more difficult to implement correctly.

Why does stream cipher fail to protect message integrity?

b) A stream cipher cannot protect message integrity because it is vulnerable to attacks in depth. For example, fund transfer messages are very highly structured.

What happens if you reuse one-time pad?

In this technique, a plaintext is paired with a random secret key (also referred to as a one-time pad). If the key is truly random, is at least as long as the plaintext, is never reused in whole or in part, and is kept completely secret, then the resulting ciphertext will be impossible to decrypt or break.

Why are stream ciphers less secure block ciphers?

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. So, they’re better suited for devices that have fewer resources.

What benefit do stream ciphers have over the one time pad?

The key typically used with a stream cipher is known as a one-time pad. Mathematically, a one-time pad is unbreakable because it’s always at least the exact same size as the message it is encrypting. A stream cipher is a cryptographic cipher to convert (encrypt) text to produce ciphertext and back.

What is the advantage of stream ciphers?

Stream ciphers work well for large or small chucks of data. They`re suitable for smaller data sizes because no block size is required. And if speed is a concern, stream ciphers are your answer, because they use a simpler transformation that typically involves an xor`d keystream.

Which of the following is a disadvantage of stream ciphers?

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.

How secure is stream cipher?

A stream cipher is an encryption technique that works byte by byte to transform plain text into code that’s unreadable to anyone without the proper key. Stream ciphers are linear, so the same key both encrypts and decrypts messages. And while cracking them can be difficult, hackers have managed to do it.

Are stream ciphers still used?

RC4 is still used today, but has shown significant weaknesses and is therefore not recommended in newer designs. The eStream project was put forth to develop new stream ciphers and the ciphers picked for the final portfolio have been well analyzed.