4 responses It's neither a stream or a block cipher. Both encrypt and decode using the same key (symmetric encryption). RSA is asymmetric, which means that you encrypt with a different key than you use to decrypt. This is necessary because otherwise anyone could encrypt messages that they then decrypted with your key.
RSA is a block cipher that supports variable-length block sizes. The fact that it is not symmetric does not preclude it from being a block or stream cipher. Furthermore, while it is not meant to be used as a block cipher, it is one. A block size of 1024 bits is common.
RSA was designed by Ron Rivest, Adi Shamir and Leonard Adleman while they were students at MIT. It is now widely used in many applications such as digital signatures, encrypted communications, etc.
Like all cryptographic algorithms, RSA's efficiency depends on its implementation. An efficient implementation should be fast enough to be useful for most applications.
In terms of speed, RSA is relatively slow compared with other ciphers available today. However, because the key length is so long (at least 768 bits), it has less risk of timing attacks. Also, since the algorithm is based on modular arithmetic, any integer factorization method can be used to attack it; this makes quantum computers a potential threat.
RSA has been successfully attacked using algebraic techniques. More recently, however, large prime factors have been discovered using computational number theory methods that are faster than previous techniques. These attacks do not require storing any data related to the keys, which makes them different from previous attacks based on supercomputers. They also show that RSA is not immune to mathematical threats.
RSA is an asymmetric cipher in which one key (your "public key") is used to encrypt and another key (your "secret key") is used to decrypt. AES is a symmetric encryption that encrypts and decrypts using the same key. While it is possible to combine these two algorithms to create a system that uses both public and secret keys, this is not done regularly.
The most important difference between RSA and AES is that RSA can be used for signing files while AES can only be used for encryption. This means that if you want to verify that a file has not been altered after being signed, you will need an additional algorithm called DSA or ECDSA. These are discussed further below.
There are other differences as well. For example, RSA is very fast to encrypt data but takes longer to decrypt it. Conversely, AES is very slow to encrypt data but can quickly decrypt large amounts of text.
Another difference is that RSA requires the use of random numbers during encryption and decryption. This is necessary because without this step, someone could learn your secret key by analyzing how much effort was required to decrypt a given message.
AES does not require random numbers and can therefore be used more efficiently. It should be noted that some implementations do use random numbers when encrypting with AES, but these are limited to preventing identical messages from producing the same encrypted value.
A block cipher is a type of encryption in which the plain text is converted one block at a time. A stream cipher, on the other hand, is a sort of encryption that performs plain text conversion by taking one byte at a time. Thus, block ciphers take multiple bytes of data as input and output multiple bytes of data, while stream ciphers take single bytes of data as input and output single bytes of data.
Block ciphers can be further divided into symmetric ciphers and asymmetric or public-key ciphers. Symmetric block ciphers use the same key to encrypt data as to decrypt it. Asymmetric ciphers use two keys: one for encryption and another for decryption. Block ciphers can also be divided into linear and non-linear types. Linear block ciphers process the entire block of data before moving on to the next block. Non-linear block ciphers will often repeat processing within the current block several times before moving on to the next block.
Stream ciphers are different from block ciphers because they operate on one bit (or one byte) at a time instead of on multiple bits (or bytes). Thus, they convert large amounts of data but cannot encrypt or decrypt individual bits. Stream ciphers include polyalphabetic, monoalphabetic, and cipher-stream algorithms.