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Security Fundamentals & Crypto · Foundational

Hybrid Cryptosystem

System that uses asymmetric cryptography to exchange a symmetric key, then symmetric encryption for bulk data.

Definition

Hybrid cryptosystems combine the key distribution advantages of asymmetric cryptography with the speed of symmetric cryptography. TLS, PGP, S/MIME, and SSH all use this approach. A digital envelope is an asymmetric-wrapped symmetric key sent with encrypted data.

Example

PGP encrypts an email with a random AES session key and encrypts that key with the recipient's public key.

Exam tip

When asked how TLS gets both speed and easy key distribution, the answer is a hybrid approach.

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