How is a ciphertext encrypted using random numbers decrypted using a symmetric key algorithm We use true random number generators as a source of keys for encryption. What I can not wrap my head around is: How is this cipher text decrypted in case of symmetric key algorithm as we need the same random number to decrypt the cipher text.

What I could guess is:


Is this random number used as a session key and transmitted using any asymmetric key algorithm?
Are PRNGs and true random number generators used as a seed?
Usually the symmetric key is exchanged with Public-key cryptography (which is asymmetric).

Quote from Wikipedia:


  Because of the computational complexity of asymmetric encryption, it is usually used only for small blocks of data, typically the transfer of a symmetric encryption key (e.g. a session key). This symmetric key is then used to encrypt the rest of the potentially long message sequence. The symmetric encryption/decryption is based on simpler algorithms and is much faster.


Concerning random-number-generators in cryptography:

Cryptographically secure pseudorandom number generators are typically used when the design of a cryptographic scheme needs a random number. These include i.e:


One-time pad
Elliptic Curve Digital Signature Algorithm
Cryptographic nonce