#------------------------------------------------------------------------------
# $File: pgp-binary-keys,v 1.2 2021/04/26 15:56:00 christos Exp $
# pgp-binary-keys: This file handles pgp binary keys.
#
# An PGP certificate or message doesn't have a fixed header.  Instead,
# they are sequences of packets:
#
#   https://tools.ietf.org/html/rfc4880#section-4.3
#
# whose order conforms to a grammar:
#
#   https://tools.ietf.org/html/rfc4880#section-11
#
# Happily most packets have a few fields that are constrained, which
# allow us to fingerprint them with relatively high certainty.
#
# A PGP packet is described by a single byte: the so-called CTB.  The
# high-bit is always set.  If bit 6 is set, then it is a so-called
# new-style CTB; if bit 6 is clear, then it is a so-called old-style
# CTB.  Old-style CTBs have only four bits of type information; bits
# 1-0 are used to describe the length.  New-style CTBs have 6 bits of
# type information.
#
# Following the CTB is the packet's length in bytes.  If we blindly
# advance the file cursor by this amount past the end of the length
# information we come to the next packet.
#
# Data Structures
# ===============
#
# New Style CTB
# -------------
#
# https://tools.ietf.org/html/rfc4880#section-4.2.2
#
#   76543210
#   ||\----/
#   ||  tag
#   |always 1
#   always 1
#
#      Tag   bits 7 and 6 set
#       0       0xC0        -- Reserved - a packet tag MUST NOT have this value
#       1       0xC1        -- Public-Key Encrypted Session Key Packet
#       2       0xC2        -- Signature Packet
#       3       0xC3        -- Symmetric-Key Encrypted Session Key Packet
#       4       0xC4        -- One-Pass Signature Packet
#       5       0xC5        -- Secret-Key Packet
#       6       0xC6        -- Public-Key Packet
#       7       0xC7        -- Secret-Subkey Packet
#       8       0xC8        -- Compressed Data Packet
#       9       0xC9        -- Symmetrically Encrypted Data Packet
#       10      0xCA        -- Marker Packet
#       11      0xCB        -- Literal Data Packet
#       12      0xCC        -- Trust Packet
#       13      0xCD        -- User ID Packet
#       14      0xCE        -- Public-Subkey Packet
#       17      0xD1        -- User Attribute Packet
#       18      0xD2        -- Sym. Encrypted and Integrity Protected Data Packet
#       19      0xD3        -- Modification Detection Code Packet
#       60 to 63 -- Private or Experimental Values
#
# The CTB is followed by the length header, which is densely encoded:
#
#   if length[0] is:
#     0..191: one byte length (length[0])
#     192..223: two byte length ((length[0] - 192) * 256 + length[2] + 192
#     224..254: four byte length (big endian interpretation of length[1..5])
#     255: partial body encoding
#
# The partial body encoding is similar to HTTP's chunk encoding.  It
# is only allowed for container packets (SEIP, Compressed Data and
# Literal).
#
# Old Style CTB
# -------------
#
#  https://tools.ietf.org/html/rfc4880#section-4.2.1
#
# CTB:
#
#   76543210
#   ||\--/\/
#   ||  |  length encoding
#   ||  tag
#   |always 0
#   always 1
#
# Tag:
#
#      Tag   bit 7 set, bits 6, 1, 0 clear
#       0       0x80        -- Reserved - a packet tag MUST NOT have this value
#       1       0x84        -- Public-Key Encrypted Session Key Packet
#       2       0x88        -- Signature Packet
#       3       0x8C        -- Symmetric-Key Encrypted Session Key Packet
#       4       0x90        -- One-Pass Signature Packet
#       5       0x94        -- Secret-Key Packet
#       6       0x98        -- Public-Key Packet
#       7       0x9C        -- Secret-Subkey Packet
#       8       0xA0        -- Compressed Data Packet
#       9       0xA4        -- Symmetrically Encrypted Data Packet
#       10      0xA8        -- Marker Packet
#       11      0xAC        -- Literal Data Packet
#       12      0xB0        -- Trust Packet
#       13      0xB4        -- User ID Packet
#       14      0xB8        -- Public-Subkey Packet
#
# Length encoding:
#
#     Value
#       0      1 byte length (following byte is the length)
#       1      2 byte length (following two bytes are the length)
#       2      4 byte length (following four bytes are the length)
#       3      indeterminate length: natural end of packet, e.g., EOF
#
# An indeterminate length is only allowed for container packets
# (SEIP, Compressed Data and Literal).
#
# Certificates
# ------------
#
# We check the first three packets to determine if a sequence of
# OpenPGP packets is likely to be a certificate.  The grammar allows
# the following prefixes:
#
#   [Primary Key] [SIG] (EOF or another certificate)
#   [Primary Key] [SIG]            [User ID]        [SIG]...
#   [Primary Key] [SIG]            [User Attribute] [SIG]...
#   [Primary Key] [SIG]            [Subkey]         [SIG]...
#   [Primary Key] [User ID]        [SIG]...
#   [Primary Key] [User Attribute] [SIG]...
#   [Primary Key] [Subkey]         [SIG]...
#
# Any number of marker packets are also allowed between each packet,
# but they are not normally used and we don't currently check for
# them.
#
# The keys and subkeys may be public or private.
#

# Key packets and signature packets are versioned.  There are two
# packet versions that we need to worry about in practice: v3 and v4.
# v4 packets were introduced in RFC 2440, which was published in 1998.
# It also deprecated v3 packets.  There are no actively used v3
# certificates (GnuPG removed the code to support them in November
# 2014).  But there are v3 keys lying around and it is useful to
# identify them.  The next version of OpenPGP will introduce v5 keys.
# The document has not yet been standardized so changes are still
# possible.  But, for our purposes, it appears that v5 data structures
# will be identical to v4 data structures modulo the version number.
#
#   https://tools.ietf.org/html/rfc2440
#   https://lists.gnupg.org/pipermail/gnupg-announce/2014q4/000358.html
#   https://www.ietf.org/id/draft-ietf-openpgp-rfc4880bis-09.html#name-key-material-packet




# The first packet has to be a public key or a secret key.
#
# New-Style Public Key
0       ubyte                   =0xC6   OpenPGP Public Key
>&0     use                     primary_key_length_new
# New-Style Secret Key
0       ubyte                   =0xC5   OpenPGP Secret Key
>&0     use                     primary_key_length_new
# Old-Style Public Key
0       ubyte&0xFC              =0x98   OpenPGP Public Key
>&-1    use                     primary_key_length_old
# Old-Style Secret Key
0       ubyte&0xFC              =0x94   OpenPGP Secret Key
>&-1    use                     primary_key_length_old

# Parse the length, check the packet's body and finally advance to the
# next packet.

# There are 4 different new-style length encodings, but the partial
# body encoding is only acceptable for the SEIP, Compressed Data, and
# Literal packets, which isn't valid for any packets in a certificate
# so we ignore it.
0               name            primary_key_length_new
>&0             ubyte           <192
#>>&0           ubyte           x               (1 byte length encoding, %d bytes)
>>&0            use             pgp_binary_key_pk_check
>>>&(&-1.B)     use             sig_or_component_1
>&0             ubyte           >191
>>&-1           ubyte           <225
# offset = ((offset[0] - 192) << 8) + offset[1] + 192 (for the length header)
# raw - (192 * 256 - 192)
# = 48960
#>>>&0          ubeshort                x       (2 byte length encoding, %d bytes)
>>>&1           use             pgp_binary_key_pk_check
>>>>&(&-2.S-48960)      use     sig_or_component_1
>&0             ubyte           =255
#>>&0           belong          x               (5 byte length encoding, %d bytes)
>>&4            use             pgp_binary_key_pk_check
>>>&(&-4.L)     use             sig_or_component_1
# Partial body encoding (only valid for container packets).
# >&0           ubyte   >224
# >>&0          ubyte           <255            partial body encoding

# There are 4 different old-style length encodings, but the
# indeterminate length encoding is only acceptable for the SEIP,
# Compressed Data, and Literal packets, which isn't valid for any
# packets in a certificate.
0               name            primary_key_length_old
#>&0            ubyte           x               (ctb: %x)
>&0             ubyte&0x3       =0
#>>&0           ubyte           x               (1 byte length encoding, %d bytes)
>>&1            use             pgp_binary_key_pk_check
>>>&(&-1.B)     use             sig_or_component_1
>&0             ubyte&0x3       =1
#>>&0           ubeshort        x               (2 byte length encoding, %d bytes)
>>&2            use             pgp_binary_key_pk_check
>>>&(&-2.S)     use             sig_or_component_1
>&0             ubyte&0x3       =2
#>>&0           ubelong x               (4 byte length encoding, %d bytes)
>>&4            use             pgp_binary_key_pk_check
>>>&(&-4.L)     use             sig_or_component_1

# Check the Key.
#
# https://tools.ietf.org/html/rfc4880#section-5.5.2
0               name            pgp_binary_key_pk_check
# Valid versions are: 2, 3, 4.  5 is proposed in RFC 4880bis.
# Anticipate a v6 / v7 format that like v5 is compatible with v4.
# key format in a decade or so :D.
>&0             ubyte           >1
>>&-1           ubyte           <8
>>>&-1          byte            x               Version %d
# Check that keys were created after 1990.
# (1990 - 1970) * 365.2524 * 24 * 60 * 60 = 631156147
>>>&0           bedate          >631156147      \b, Created %s
>>>>&-5         ubyte           >3
>>>>>&4         use             pgp_binary_key_algo
>>>>&-5         ubyte           <4
>>>>>&6         use             pgp_binary_key_algo

# Print out the key's algorithm and the number of bits, if this is
# relevant (ECC keys are a fixed size).
0               name            pgp_binary_key_algo
>0              clear           x
>&0             ubyte           =1      \b, RSA (Encrypt or Sign,
>>&0            ubeshort        x       \b %d bits)
>&0             ubyte           =2      \b, RSA (Encrypt,
>>&0            ubeshort        x       \b %d bits)
>&0             ubyte           =3      \b, RSA (Sign,
>>&0            ubeshort        x       \b %d bits)
>&0             ubyte           =16     \b, El Gamal (Encrypt,
>>&0            ubeshort        x       \b %d bits)
>&0             ubyte           =17     \b, DSA
>>&0            ubeshort        x       \b (%d bits)
>&0             ubyte           =18     \b, ECDH
>&0             ubyte           =19     \b, ECDSA
>&0             ubyte           =20     \b, El Gamal (Encrypt or Sign,
>>&0            ubeshort        x       \b %d bits)
>&0             ubyte           =22     \b, EdDSA
>&0             default         x
>>&0            ubyte           x       \b, Unknown Algorithm (%#x)

# Match all possible second packets.
0       name            sig_or_component_1
#>0     ubyte           x       (ctb: %x)
>&0     ubyte           =0xC2
>>0     ubyte           x       \b; Signature
>>&0    use             sig_or_component_1_length_new
>&0     ubyte           =0xCD
>>0     ubyte           x       \b; User ID
>>&0    use             sig_or_component_1_length_new
>&0     ubyte           =0xCE
>>0     ubyte           x       \b; Public Subkey
>>&0    use             sig_or_component_1_length_new
>&0     ubyte           =0xC7
>>0     ubyte           x       \b; Secret Subkey
>>&0    use             sig_or_component_1_length_new
>&0     ubyte           =0xD1
>>0     ubyte           x       \b; User Attribute
>>&0    use             sig_or_component_1_length_new
>&0     ubyte&0xFC      =0x88
>>0     ubyte           x       \b; Signature
>>&-1   use             sig_or_component_1_length_old
>&0     ubyte&0xFC      =0xB4
>>0     ubyte           x       \b; User ID
>>&-1   use             sig_or_component_1_length_old
>&0     ubyte&0xFC      =0xB8
>>0     ubyte           x       \b; Public Subkey
>>&-1   use             sig_or_component_1_length_old
>&0     ubyte&0xFC      =0x9C
>>0     ubyte           x       \b; Secret Subkey
>>&-1   use             sig_or_component_1_length_old

# Copy of 'primary_key_length_new', but calls cert_packet_3.
0               name            sig_or_component_1_length_new
>&0             ubyte           <192
#>>&0           ubyte           x               (1 byte new length encoding, %d bytes)
>>&(&-1.B)      use             cert_packet_3
>&0             ubyte           >191
>>&-1           ubyte           <225
# offset = ((offset[0] - 192) << 8) + offset[1] + 192 + 1 (for the length header)
# raw - (192 * 256 - 192 - 1)
# = 48959
#>>>&-1         ubeshort                x       (2 byte new length encoding, %d bytes)
>>>&(&-1.S-48959)       use     cert_packet_3
>&0             ubyte           =255
#>>&0           belong          x               (5 byte new length encoding, %d bytes)
>>&(&-4.L)      use             cert_packet_3
# Partial body encoding (only valid for container packets).
# >&0           ubyte   >224
# >>&0          ubyte           <255            partial body encoding

0               name            sig_or_component_1_length_old
#>&0            ubyte           x               (ctb: %x)
>&0             ubyte&0x3       =0
#>>&0           ubyte           x               (1 byte old length encoding, %d bytes)
>>&(&0.B+1)     use             cert_packet_3
>&0             ubyte&0x3       =1
#>>&0           ubeshort        x               (2 byte old length encoding, %d bytes)
>>&(&0.S+2)     use             cert_packet_3
>&0             ubyte&0x3       =2
#>>&0           ubelong x               (4 byte old length encoding, %d bytes)
>>&(&0.L+4)     use             cert_packet_3

# Copy of above.
0       name            cert_packet_3
#>0     ubyte           x       (ctb: %x)
>&0     ubyte           =0xC2
>>0     ubyte           x       \b; Signature
>>&0    use             cert_packet_3_length_new
>&0     ubyte           =0xCD
>>0     ubyte           x       \b; User ID
>>&0    use             cert_packet_3_length_new
>&0     ubyte           =0xCE
>>0     ubyte           x       \b; Public Subkey
>>&0    use             cert_packet_3_length_new
>&0     ubyte           =0xC7
>>0     ubyte           x       \b; Secret Subkey
>>&0    use             cert_packet_3_length_new
>&0     ubyte           =0xD1
>>0     ubyte           x       \b; User Attribute
>>&0    use             cert_packet_3_length_new
>&0     ubyte&0xFC      =0x88
>>0     ubyte           x       \b; Signature
>>&-1   use             cert_packet_3_length_old
>&0     ubyte&0xFC      =0xB4
>>0     ubyte           x       \b; User ID
>>&-1   use             cert_packet_3_length_old
>&0     ubyte&0xFC      =0xB8
>>0     ubyte           x       \b; Public Subkey
>>&-1   use             cert_packet_3_length_old
>&0     ubyte&0xFC      =0x9C
>>0     ubyte           x       \b; Secret Subkey
>>&-1   use             cert_packet_3_length_old

# Copy of above.
0               name            cert_packet_3_length_new
>&0             ubyte           <192
#>>&0           ubyte           x               (1 byte new length encoding, %d bytes)
>>&(&-1.B)      use             pgp_binary_keys_end
>&0             ubyte           >191
>>&-1           ubyte           <225
# offset = ((offset[0] - 192) << 8) + offset[1] + 192 + 1 (for the length header)
# raw - (192 * 256 - 192 - 1)
# = 48959
#>>>&-1         ubeshort                x       (2 byte new length encoding, %d bytes)
>>>&(&-1.S-48959)       use     pgp_binary_keys_end
>&0             ubyte           =255
#>>&0           belong          x               (5 byte new length encoding, %d bytes)
>>&(&-4.L)      use             pgp_binary_keys_end

0               name            cert_packet_3_length_old
#>&0            ubyte           x               (ctb: %x)
>&0             ubyte&0x3       =0
#>>&0           ubyte           x               (1 byte old length encoding, %d bytes)
>>&(&0.B+1)     use             pgp_binary_keys_end
>&0             ubyte&0x3       =1
#>>&0           ubeshort        x               (2 byte old length encoding, %d bytes)
>>&(&0.S+2)     use             pgp_binary_keys_end
>&0             ubyte&0x3       =2
#>>&0           ubelong x               (4 byte old length encoding, %d bytes)
>>&(&0.L+4)     use             pgp_binary_keys_end

# We managed to parse the first three packets of the certificate.  Declare
# victory.
0               name            pgp_binary_keys_end
>0              byte            x               \b; OpenPGP Certificate
!:mime          application/pgp-keys
!:ext           pgp/gpg/pkr/asd

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