#------------------------------------------------------------------------------ # $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