It provides the basic definitions of and recommendations for implementing the RSA algorithm for public-key cryptography.
It defines the mathematical properties of public and private keys, primitive operations for encryption and signatures, secure cryptographic schemes, and related ASN.1 syntax representations.
Compared to 2.1 (2002-06-14), which was republished as RFC 3447, version 2.2 updates the list of allowed hashing algorithms to align them with FIPS 180-4, therefore adding SHA-224, SHA-512/224 and SHA-512/256.
The PKCS #1 standard defines the mathematical definitions and properties that RSA public and private keys must have.
The traditional key pair is based on a modulus, n, that is the product of two distinct large prime numbers, p and q, such that
Starting with version 2.1, this definition was generalized to allow for multi-prime keys, where the number of distinct primes may be two or more.
When dealing with multi-prime keys, the prime factors are all generally labeled as
Although mathematically redundant to the compact form, the additional terms allow for certain computational optimizations when using the key.
The primitive operations provide the fundamental instructions for turning the raw mathematical formulas into computable algorithms.
The concept of a cryptographic scheme is to define higher level algorithms or uses of the primitives so they achieve certain security goals.
[4][5] PKCS #1 was subsequently updated in the release 2.0 and patches were issued to users wishing to continue using the old version of the standard.