ITPEC FE Morning April 2019 Question 40

RSA — a public key algorithm: data encrypted with the public key can be decrypted only with the matching private key.

The security of RSA rests on how hard it is to factor the product of two large primes. Anyone may hold the public key and encrypt; only the owner of the private key can decrypt. The same key pair also supports digital signatures, where the private key signs and the public key verifies.

Answer (c)

Why not others:

• •(a) AES — a symmetric (common key) block cipher: the same secret key encrypts and decrypts
• •(b) KCipher-2 — a symmetric stream cipher, standardised in ISO/IEC 18033-4; again one shared key
• •(d) SHA-256 — a hash function that produces a 256-bit digest; it is one-way and uses no key, so it is not encryption at all

Key rule: Sort algorithms into three families: public key (RSA, elliptic curve), common key (AES, DES, KCipher-2) and hash (SHA-2, SHA-3); only a public/private key pair makes a cipher public key.

Security · AI-written, may contain errors