Cambridge O Level Computer Science · Syllabus 2210 · Data Transmission
Asymmetric Encryption
What is Asymmetric Encryption?
Asymmetric encryption uses two mathematically related keys: a public key that may be shared and is used to encrypt data for its owner, and a private key that is kept secret by its owner and is used to decrypt that data.
This definition is part of the Data Transmission chapter in Cambridge O Level Computer Science.
Asymmetric Encryption in context
Asymmetric encryption uses two mathematically related keys: a public key, which may be shared with anyone, and a private key, which must be kept secret by its owner and is never transmitted. In the confidentiality model used by this syllabus, the recipient publishes their public key; a sender encrypts the plaintext using the recipient's public key; the ciphertext is transmitted; and the recipient decrypts it using their own private key. The public key that encrypted the message cannot decrypt it — which is exactly why it is safe to publish, and why asymmetric encryption solves the key-distribution problem that symmetric encryption creates.
Questions students ask about Asymmetric Encryption
What is the difference between symmetric and asymmetric encryption?
In symmetric encryption, the same secret key encrypts and decrypts the data, so both parties must hold that key and it must be exchanged securely beforehand. In asymmetric encryption, two mathematically related keys are used: a public key, which may be shared with anyone and encrypts data for its owner, and a private key, kept secret by its owner and used to decrypt it. Because the public key that encrypts a message cannot decrypt it, asymmetric encryption avoids the problem of exchanging a secret key securely.