PKCS7

PKCS #7 (PKCS7, Cryptographic Message Syntax Standard) defines standard formats for messages secured using public-key cryptography. S/MIME, a format for secure e-mail messages, is based in part on PKCS7.

As of version 1.5, PKCS7 defines six content types:
 * Data
 * Signed data
 * Enveloped data
 * Signed-and-enveloped data
 * Digested data
 * Encrypted data

Specifications

 * RFC 2315: PKCS #7: Cryptographic Message Syntax, Version 1.5

Software

 * OpenSSL