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In symmetric key cryptography, both parties must possess a secret key which they must exchange prior to using any encryption.Distribution of secret keys has been problematic until recently, because it involved face-to-face meeting, use of a trusted courier, or sending the key through an existing encryption channel.
Symmetric-key encryption: the same key is used for both encryption and decryption. Symmetric-key algorithms [a] are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between the two keys. [1]
McEliece consists of three algorithms: a probabilistic key generation algorithm that produces a public and a private key, a probabilistic encryption algorithm, and a deterministic decryption algorithm. All users in a McEliece deployment share a set of common security parameters: ,,.
Note that for very long messages the bulk of the work in encryption/decryption is done by the more efficient symmetric-key scheme, while the inefficient public-key scheme is used only to encrypt/decrypt a short key value. [3] All practical implementations of public key cryptography today employ the use of a hybrid system.
Public key transport keys are the public keys of asymmetric key pairs that are used to encrypt keys using a public key algorithm. These keys are used to establish keys (e.g., key wrapping keys, data encryption keys or MAC keys) and, optionally, other keying material (e.g., Initialization Vectors). Symmetric key agreement key
Crypto systems using asymmetric key algorithms do not evade the problem either. That a public key can be known by all without compromising the security of an encryption algorithm (for some such algorithms, though not for all) is certainly useful, but does not prevent some kinds of attacks.
A key can directly be generated by using the output of a Random Bit Generator (RBG), a system that generates a sequence of unpredictable and unbiased bits. [10] A RBG can be used to directly produce either a symmetric key or the random output for an asymmetric key pair generation.
The encryption algorithm implements an XOR-based stream cipher using the Blum-Blum-Shub (BBS) pseudo-random number generator to generate the keystream. Decryption is accomplished by manipulating the final state of the BBS generator using the private key , in order to find the initial seed and reconstruct the keystream.