What Is a Stream Cipher?

Use the key to generate a key stream Z = Z1Z2Z3 ..., and then use this key stream to sequentially encrypt the plaintext X = X0X1X2 .... The resulting password is a serial password, also known as a stream password. The key stream is generated by the key stream generator f: zi = f (k, si), where si is the state of the memory (memory element) in the encryptor at time i, and k is the key. The development of the serial cipher scheme is an attempt to imitate the "one-time-one-pass" system.

Use the key to generate a key stream Z = Z1Z2Z3 ..., and then use this key stream to sequentially encrypt the plaintext X = X0X1X2 .... The resulting password is a serial password, also known as a stream password. The key stream is generated by the key stream generator f: zi = f (k, si), where si is the state of the memory (memory element) in the encryptor at time i, and k is the key. The development of the serial cipher scheme is an attempt to imitate the "one-time-one-pass" system.

Chinese name

Serial password

Foreign name

Stream Cipher

nickname

Stream cipher

Category

Symmetric cryptographic algorithm

Sequence cipher is also called Stream Cipher, which is a kind of symmetric cipher algorithm. The serial cipher has the characteristics of simple implementation, easy hardware implementation, fast encryption and decryption processing, and no or only limited error propagation, so it maintains advantages in practical applications, especially in dedicated or confidential institutions. Typical application areas include wireless communications And diplomatic communications. In 1949, Shannon proved that the one-time password system was absolutely secure. This gave strong support to the study of sequence cryptography. The development of the sequence password scheme was an attempt to imitate the one-time password system, or "one-time password" The cryptographic scheme is the rudimentary of sequential cryptography. If the sequence cipher uses a key stream with the same length as the message stream in a truly random manner, then the sequence cipher at this time is a one-time one-pass cryptosystem. If a random sequence (keystream) can be generated in a way, and this sequence is determined by the key, then such a sequence can be used for encryption, that is, the key and the plain text are represented as continuous symbols or binary, corresponding For encryption, one or more bits in plain text are processed at one time during encryption and decryption.

In the sequence cipher, the key stream is generated by the key stream generator f: zi = f (k, si), where si is the state of the memory (memory element) in the encryptor at time i. According to whether the storage state of the memory element si in the encryptor depends on the plain text characters, the serial password can be further divided into two types of synchronization and self-synchronization. If si is independent of clear text characters, it is called a synchronous stream cipher, otherwise it is called a self-sync stream cipher.

Comparison of serial cipher and block cipher

Block ciphers use a certain size as the basic unit for each processing, while sequence ciphers use one element (a letter or a bit) as the basic processing unit.

Sequence cipher is a time-varying cryptographic transformation. It has the advantages of fast conversion speed, low error propagation, and simpler hardware implementation circuit. Its disadvantages are: low diffusion (meaning insufficient confusion), and insensitivity to insertion and modification.

The block cipher uses a fixed transformation that does not change with time. It has the advantages of good diffusion and insertion sensitivity. Its disadvantages are: slow encryption and decryption processing, and error propagation.

Sequence cryptography involves a large amount of theoretical knowledge, has proposed many design principles, and has been extensively analyzed, but many research results have not been fully disclosed. This may be because sequence cryptography is currently mainly used in military and diplomatic secret departments . At present, the published sequence cipher algorithms mainly include RC4 and SEAL.