View Source OpenPGP.Util.PKCS1 (OpenPGP v0.6.2)

Utility functions for PKCS#1 encoding/decoding

RFC4880

13.1. PKCS#1 Encoding in OpenPGP

This standard makes use of the PKCS#1 functions EME-PKCS1-v1_5 and EMSA-PKCS1-v1_5. However, the calling conventions of these functions has changed in the past. To avoid potential confusion and interoperability problems, we are including local copies in this document, adapted from those in PKCS#1 v2.1 [RFC3447]. RFC 3447 should be treated as the ultimate authority on PKCS#1 for OpenPGP. Nonetheless, we believe that there is value in having a self- contained document that avoids problems in the future with needed changes in the conventions.

Summary

Functions

encode(atom, message, key)

Encode message as described in PKCS#1 block encoding EME-PKCS1-v1_5 in Section 7.2.1 of RFC3447

Functions

Link to this function

encode(atom, message, key)

View Source 
@spec encode(:eme_pkcs1_v1_5, message :: binary(), key :: binary()) ::
  encoded_message :: binary()

Encode message as described in PKCS#1 block encoding EME-PKCS1-v1_5 in Section 7.2.1 of RFC3447

Example 

iex> key = :crypto.strong_rand_bytes(16)
...> em = OpenPGP.Util.PKCS1.encode(:eme_pkcs1_v1_5, "Hello", key)
...> <<0x00::8, 0x02::8, _::64, 0x00::8, "Hello">> = em 

iex> key = :crypto.strong_rand_bytes(15)
...> OpenPGP.Util.PKCS1.encode(:eme_pkcs1_v1_5, "Hello", key)
** (RuntimeError) message too long

See Section 13.1 of [RFC4880] for notes on OpenPGP's use of PKCS#1.

13.1.1. EME-PKCS1-v1_5-ENCODE

Input: k = the length in octets of the key modulus M = message to be encoded, an octet string of length mLen, where

   mLen <= k - 11

Output: EM = encoded message, an octet string of length k Error: "message too long"

  1. Length checking: If mLen > k - 11, output "message too long" and stop.

  2. Generate an octet string PS of length k - mLen - 3 consisting of pseudo-randomly generated nonzero octets. The length of PS will be at least eight octets.

  3. Concatenate PS, the message M, and other padding to form an encoded message EM of length k octets as

    EM = 0x00 || 0x02 || PS || 0x00 || M.

  4. Output EM.