- 2074 Magh · 4 marks
Short note: PGP
Short answer
PGP combines hashing, public-key signing, and symmetric encryption to provide confidentiality, authentication, integrity, and compression. It uses a web of trust for key management and Radix-64 encoding to ensure email compatibility.
Write a short note on PGP.
Pretty Good Privacy (PGP) is an e-mail and file security program designed by Phil Zimmermann in 1991. It provides confidentiality, authentication, integrity and compression using a mix of public-key and symmetric cryptography. Its standard form is OpenPGP (RFC 4880); GnuPG is a free implementation.
Services and how they work
- Authentication / integrity: the sender hashes the message (SHA) and encrypts the digest with his private key (RSA/DSS). The receiver decrypts with the sender's public key and compares digests.
- Confidentiality: the message is encrypted with a random one-time session key using a symmetric cipher (AES, 3DES, CAST-128); the session key is encrypted with the receiver's public key (RSA).
- Compression: ZIP is applied after signing and before encryption.
- E-mail compatibility: binary output is converted to ASCII with Radix-64.
- Segmentation: long messages are split to match mail size limits.
Key management: each user has a public key ring and a private key ring. Trust is built by a web of trust: users sign others' public keys, instead of relying on a central certificate authority.
M -> Hash -> Sign(KR_A) -> ZIP -> Enc(KS) -> Radix64 -> SMTP
KS -> Enc(KU_B) ----^
Use: secure e-mail, file encryption, software signing.
✓ Answer checked by Claude Opus 5.5 (high effort)