View Source OpenPGP

OpenPGP lib allows to inspect, decode and decrypt OpenPGP Message Format as per RFC4880

Installation

Add :open_pgp to the list of dependencies in mix.exs:

def deps() do
  [
    {:open_pgp, "~> 0.5"}
  ]
end

OpenPGP Packet

The OpenPGP.Packet is a generic packet type. It has an essential purpose: split OpenPGP message in packets and decode packet tags.

An OpenPGP message is constructed from a number of records that are traditionally called packets. A packet is a chunk of data that has a tag specifying its meaning. An OpenPGP message, keyring, certificate, and so forth consists of a number of packets. Some of those packets may contain other OpenPGP packets (for example, a compressed data packet, when uncompressed, contains OpenPGP packets). Each packet consists of a packet header, followed by the packet body. For more details refer to Packet Syntax chapter in RFC4880

Once OpenPGP message split into generic packets, the higher order tag-specific packet decoders can be applied on its' data. Example:

{packet, _rest} = OpenPGP.Packet.decode("...")

{compressed_data_packet, <<>>} =
  packet |> OpenPGP.Util.concat_body() |> OpenPGP.CompressedDataPacket.decode()

More details can be found in OpenPGP.Packet and OpenPGP.Packet.Behaviour

Examples

List and cast packets

List packets in a message and then cast to specific packet types.

iex> message = <<160, 24, 2, 120, 156, 243, 72, 205, 201, 201, 215, 81, 8, 207, 47, 202, 73, 81, 84, 84, 4, 0, 40, 213, 4, 172>>
...>
iex> packets = OpenPGP.list_packets(message)
[
  %OpenPGP.Packet{
    body: [
      %OpenPGP.Packet.BodyChunk{
        chunk_length: {:fixed, 24},
        data: <<2, 120, 156, 243, 72, 205, 201, 201, 215, 81, 8, 207, 47, 202, 73, 81, 84, 84, 4, 0, 40, 213, 4, 172>>,
        header_length: 1
      }
    ],
    tag: %OpenPGP.Packet.PacketTag{
      format: :old,
      length_type: {0, "one-octet"},
      tag: {8, "Compressed Data Packet"}
    }
  }
]
iex> OpenPGP.cast_packets(packets)
[
  %OpenPGP.CompressedDataPacket{
    algo: {2, "ZLIB [RFC1950]"},
    data_deflated: <<120, 156, 243, 72, 205, 201, 201, 215, 81, 8, 207, 47, 202, 73, 81, 84, 84, 4, 0, 40, 213, 4, 172>>,
    data_inflated: "Hello, World!!!"
  }
]

Decode Generic OpenPGP packet

In this example the packet tag specifies a Signature Packet with body length of 7 bytes. The remaining binary will be return as a second element in a two element tuple. More details in OpenPGP.Packet.Behaviour.

iex> alias OpenPGP.Packet
iex> alias OpenPGP.Packet.PacketTag
iex> alias OpenPGP.Packet.BodyChunk
iex> Packet.decode(<<1::1, 0::1, 2::4, 0::2, 7::8, "Hello, World!!!">>)
{
  %Packet{
    tag: %PacketTag{format: :old, length_type: {0, "one-octet"}, tag: {2, "Signature Packet"}},
    body: [%BodyChunk{chunk_length: {:fixed, 7}, data: "Hello, ", header_length: 1}]
  },
  "World!!!"
}

CompressedDataPacket

The OpenPGP.CompressedDataPacket will inflate data implicitly when decoded (also, data inflated implicitly when OpenPGP.cast_packets/1 used).

iex> alias OpenPGP.CompressedDataPacket
iex> deflated = <<120, 156, 243, 72, 205, 201, 201, 215, 81, 8, 207, 47, 202, 73, 81, 84, 84, 4, 0, 40, 213, 4, 172>>
iex> CompressedDataPacket.decode(<<2, deflated::binary>>)
{
  %CompressedDataPacket{
    algo: {2, "ZLIB [RFC1950]"},
    data_deflated: deflated,
    data_inflated: "Hello, World!!!"},
  <<>>
}

IntegrityProtectedDataPacket

The OpenPGP.IntegrityProtectedDataPacket does not decrypt its' data implicitly. The OpenPGP.IntegrityProtectedDataPacket.decrypt/2 should be used to get plaintext. Please note that some packets have packet speicifc functions, such as OpenPGP.IntegrityProtectedDataPacket.decrypt/2.

iex> alias OpenPGP.IntegrityProtectedDataPacket
iex> alias OpenPGP.PublicKeyEncryptedSessionKeyPacket
...>
iex> key = <<38, 165, 130, 172, 168, 51, 184, 238, 96, 204, 88,
...>   134, 93, 25, 162, 22, 83, 211, 140, 176, 115, 113, 37, 201,
...>   171, 249, 115, 64, 94, 59, 35, 60>>
...>
iex> iv = <<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>>
iex> <<prefix::14*8, chsum::2*8>> = :crypto.strong_rand_bytes(16)
iex> plaintext = <<prefix::14*8, chsum::2*8, chsum::2*8, "Hello">>
...>
iex> ciphertext =
...>   :crypto.crypto_one_time(
...>    :aes_256_cfb128,
...>    key,
...>    iv,
...>    plaintext,
...>    true)
...>
iex> payload = <<1::8, ciphertext::binary>>
iex> {packet_decoded, <<>>} = IntegrityProtectedDataPacket.decode(payload)
{
  %IntegrityProtectedDataPacket{
    ciphertext: ciphertext,
    plaintext: nil,
    version: 1
  },
  <<>>
}
iex> pkesk = %PublicKeyEncryptedSessionKeyPacket{
...>   version: 3,
...>   session_key_algo: {9, "AES with 256-bit key"},
...>   session_key_material: {key}
...> }
...>
iex> IntegrityProtectedDataPacket.decrypt(packet_decoded, pkesk)
%IntegrityProtectedDataPacket{
  version: 1,
  plaintext: "Hello",
  ciphertext: ciphertext
}

Notes

As of v0.5.x:

  1. Any valid OpenPGP message can be decoded via generic OpenPGP.Packet decoder. This abstraction layer provide Packet Tags and Body Chunks for packet envelope level evaluation.
  2. Some Packet Tag specific decoders implemented with limited feature support:
    1. OpenPGP.LiteralDataPacket
    2. OpenPGP.PublicKeyEncryptedSessionKeyPacket
    3. OpenPGP.PublicKeyPacket - support only V4 packets
    4. OpenPGP.SecretKeyPacket - support only V4 packets; Iterated and Salted String-to-Key (S2K) specifier (ID: 3); S2K usage convention octet of 254 only; S2K hashing algo SHA1; AES128 symmetric encryption of secret key material
    5. OpenPGP.CompressedDataPacket - support only ZLIB- and ZIP-style blocks
    6. OpenPGP.IntegrityProtectedDataPacket - support Session Key algo 9 (AES with 256-bit key) in CFB mode; Modification Detection Code system is not supported

At a high level OpenPGP.list_packets/1 and OpenPGP.cast_packets/1 serve as an entrypoint to OpenPGP Message decoding and extracting generic data.

Packet specific decoders implement OpenPGP.Packet.Behaviour, which exposes .decode/1 interface (including genric OpenPGP.Packet). Additionaly some of the packet specific decoders may provide interface for further packet processing, such as OpenPGP.SecretKeyPacket.decrypt/2.

Usage example of a comon use case can be found in test/open_pgp/open_pgp_test.exs in the test "full integration: load private key and decrypt encrypted file"

Refs, Snippets, Misc 

# GPG commands
~$ gpg --list-keys
~$ gpg --list-secret-keys
~$ gpg --export-secret-key --armor john.doe@example.com > ./private.pgp
~$ gpg --list-packets --verbose example.txt.pgp
~$ gpg --encrypt --recipient F89B64F782254B03624FCF5C052E8381B5C335DA /usr/share/dict/words
~$ gpg --batch --passphrase "passphrase" --quick-generate-key "John Doe (RSA2048) <john.doe@example.com>" rsa2048 default never
~$ gpg --edit-key F89B64F782254B03624FCF5C052E8381B5C335DA

# Handy tools
~$ hexdump -vx ./words.pgp
~$ xxd -b ./words.pgp
~$ xxd -g 1