22 \h'-\w'\\$1\ 'u'\\$1\ \c
27 .TH catcrypt 1 "30 September 2004" "Straylight/Edgeware" "Catacomb cryptographic library"
29 catcrypt \- encrypt and decrypt messages
86 command encrypts and decrypts messages. It also works as a simple PEM
87 encoder and decoder. It provides a number of subcommands, by which the
88 various operations may be carried out.
90 Before the command name,
92 may be given. The following global options are supported:
94 .BR "\-h, \-\-help " [ \fIcommand ...]
95 Writes a brief summary of
97 various options to standard output, and returns a successful exit
98 status. With command names, gives help on those commands.
100 .B "\-v, \-\-version"
101 Writes the program's version number to standard output, and returns a
102 successful exit status.
105 Writes a very terse command line summary to standard output, and returns
106 a successful exit status.
108 .BI "\-k, \-\-keyring " file
109 Names the keyring file which
111 is to process. The default keyring, used if this option doesn't specify
112 one, is the file named
114 in the current directory. See
118 for more details about keyring files.
120 Algorithms to be used with a particular key are described by attributes
121 on the key, or its type. The
123 command deals with both signing and key-encapsulation keys. (Note that
125 uses signing keys in the same way as
127 .SS "Key-encapsulation keys"
128 (Key encapsulation is a means of transmitting a short, known, random
129 secret to a recipient. It differs from encryption in technical ways
130 which are largely uninteresting at this point.)
150 attribute is present on the key, then it must have this form; otherwise,
151 the key's type must have the form
154 Algorithm selections are taken from appropriately-named attributes, or,
155 failing that, from the
158 The key-encapsulation mechanism is chosen according to the setting of
162 for a list of supported KEMs.
165 This is Shoup's RSA-KEM (formerly Simple RSA); see
167 A proposal for an ISO standard for public key encryption (version 2.0)
169 .BR http://eprint.iacr.org/2000/060/ .
179 This is standard Diffie-Hellman key exchange, hashing the resulting
180 shared secret to form the key, as used in, e.g., DLIES (P1363a).
185 command, preferably with the
187 options, to generate the key.
190 This is the elliptic-curve analogue of
196 command to generate the key.
199 This is a simple symmetric encapsulation scheme. It works by hashing a
200 binary key with a randomly-generated salt. Use the
209 This is Bernstein's Curve25519, a fast Diffie-Hellman using a specific
221 This is Hamburg's Curve25519, a strong Diffie-Hellman using a specific
232 The bulk crypto transform is chosen based on the
234 attribute on the key, or, failing that,
240 .B catcrypt show bulk
241 for a list of supported bulk crypto transforms.
244 A generic composition of
245 a cipher secure against chosen-plaintext attack,
246 and a message authentication code.
252 .B catcrypt show cipher
253 for a list of supported symmetric encryption algorithms; the default
257 This is the default transform.
260 Use an `authenticated encryption with additional data' (AEAD) scheme.
261 The specific scheme is named by the
264 .B catcrypt show aead
265 for a list of supported AEAD schemes; the default is
266 .BR chacha20-poly1305 .
269 Use Salsa20 or ChaCha and Poly1305 to secure the bulk data.
270 This is nearly the same as the NaCl
275 uses Salsa20 or ChaCha rather than XSalsa20,
276 because it doesn't need the latter's extended nonce.
279 attribute may be set to one of
290 As well as the KEM itself, a number of supporting algorithms are used.
291 These are taken from appropriately named attributes on the key or,
292 failing that, derived from other attributes as described below.
295 This is the symmetric encryption algorithm
296 used by the bulk data transform.
303 is used; if that it absent, then the default depends on the bulk
307 This is the hash function used to distil entropy from the shared secret
308 constructed by the raw KEM. If there is no
314 is used; if that is absent then the default of
317 .B catcrypt show hash
318 for a list of supported symmetric encryption algorithms.
321 This is the message authentication algorithm
325 to ensure integrity of the encrypted message and
326 defend against chosen-ciphertext attacks.
331 is chosen as a default. Run
333 for a list of supported message authentication algorithms.
336 This is the key derivation function used to stretch the hashed shared
337 secret to a sufficient length to select symmetric encryption and
338 authentication keys, initialization vectors and other necessary
339 pseudorandom quantities. If there is no
343 is chosen as a default. Run
345 for a list of supported key derivation functions.
347 Not all supported functions have the required security features: don't
348 override the default choice unless you know what you're doing.
358 attribute is present on the key, then it must have this form; otherwise,
359 the key's type must have the form
362 Algorithm selections are taken from appropriately-named attributes, or,
363 failing that, from the
366 The signature algorithm is chosen according to the setting of
370 for a list of supported signature algorithms.
373 This is almost the same as the RSASSA-PKCS1-v1_5 algorithm described in
374 RFC3447; the difference is that the hash is left bare rather than being
375 wrapped in a DER-encoded
377 structure. This doesn't affect security since the key can only be used
378 with the one hash function anyway, and dropping the DER wrapping permits
379 rapid adoption of new hash functions. Regardless, use of this algorithm
380 is not recommended, since the padding method has been shown vulnerable
390 This is the RSASSA-PSS algorithm described in RFC3447. It is the
391 preferred RSA-based signature scheme. Use the
400 This is the DSA algorithm described in FIPS180-1 and FIPS180-2. Use the
409 This is the ECDSA algorithm described in ANSI X9.62 and FIPS180-2. Use
419 This is the revised KCDSA (Korean Certificate-based Digital Signature
420 Algorithm) described in
421 .I The Revised Version of KCDSA
422 .RB ( http://dasan.sejong.ac.kr/~chlim/pub/kcdsa1.ps ).
434 This is an unofficial elliptic-curve analogue of the KCDSA algorithm.
444 This is Bernstein, Duif, Lange, Schwabe, and Yang's Ed25519 algorithm.
445 More specifically, this is HashEd25519
448 algorithm \(en by default
460 This is Bernstein, Duif, Lange, Schwabe, and Yang's EdDSA algorithm,
461 using Hamburg's Ed448-Goldilocks elliptic curve,
462 as specified in RFC8032.
463 More specifically, this is HashEd448
466 algorithm \(en by default
478 This uses a symmetric message-authentication algorithm rather than a
479 digital signature. The precise message-authentication scheme used is
482 attribute on the key, which defaults to
484 if unspecified. Use the
492 As well as the signature algorithm itself, a hash function is used.
493 This is taken from the
495 attribute on the key, or, failing that, from the
499 or, if that is absent, determined by the signature algorithm as follows.
507 the default hash function is
514 the default hash function is
518 the default hash function is
522 the default hash function is
526 .B catcrypt show hash
527 for a list of supported hash functions.
529 Two encodings for the ciphertext are supported.
532 The raw format, which has the benefit of being smaller, but needs to be
533 attached to mail messages and generally handled with care.
536 PEM-encapsulated Base-64 encoded text. This format can be included
537 directly in email and picked out again automatically; but there is a
538 4-to-3 data expansion as a result.
539 .SH "COMMAND REFERENCE"
543 command behaves exactly as the
545 option. With no arguments, it shows an overview of
547 options; with arguments, it describes the named subcommands.
551 command prints various lists of tokens understood by
553 With no arguments, it prints all of the lists; with arguments, it prints
554 just the named lists, in order. The recognized lists can be enumerated
559 command. The lists are as follows.
562 The lists which can be enumerated by the
567 The key-encapsulation algorithms which can be used in a
568 key-encapsulation key's
573 The symmetric encryption algorithms which can be named in a
574 key-encapsulation key's
576 attribute when using the
581 The message authentication algorithms which can be named in a
582 key-encapsulation key's
587 The signature algorithms which can be named in a signing key's
592 The hash functions which can be named in a key's
597 The encodings which can be applied to encrypted messages; see
603 command encrypts a file and writes out the appropriately-encoded
604 ciphertext. By default, it reads from standard input and writes to
605 standard output. If a filename argument is given, this file is read
606 instead (as binary data).
608 The following options are recognized.
611 Produce ASCII-armoured output. This is equivalent to specifying
617 .BI "\-f, \-\-format " format
618 Produce output encoded according to
621 .BI "\-k, \-\-key " tag
622 Use the key-encapsulation key named
624 in the current keyring; the default key is
627 .BI "\-p, \-\-progress"
628 Write a progress meter to standard error while processing large files.
630 .BI "\-s, \-\-sign-key " tag
631 Use the signature key named
633 in the current keyring; the default is not to sign the ciphertext.
635 .BI "\-o, \-\-ouptut " file
638 rather than to standard output.
640 .B "\-C, \-\-nocheck"
641 Don't check the public key for validity. This makes encryption go much
642 faster, but at the risk of using a duff key.
646 command decrypts a ciphertext and writes out the plaintext. By default,
647 it reads from standard input and writes to standard output. If a
648 filename argument is given, this file is read instead.
650 The following options are recognized.
653 Read ASCII-armoured input. This is equivalent to specifying
660 Buffer plaintext data until we're sure we've got it all. This is forced
661 on if output is to stdout, but is always available as an option.
663 .BI "\-f, \-\-format " format
664 Read input encoded according to
667 .BI "\-p, \-\-progress"
668 Write a progress meter to standard error while processing large files.
670 .B "\-v, \-\-verbose"
671 Produce more verbose messages. See below for the messages produced
672 during decryption. The default verbosity level is 1. (Currently this
673 is the most verbose setting. This might not be the case always.)
676 Produce fewer messages.
678 .BI "\-o, \-\-output " file
681 instead of to standard output. The file is written in binary mode.
682 Fixing line-end conventions is your problem; there are lots of good
683 tools for dealing with it.
685 .B "\-C, \-\-nocheck"
686 Don't check the private key for validity. This makes decryption go much
687 faster, but at the risk of using a duff key, and possibly leaking
688 information about the private key.
690 Output is written to standard output in a machine-readable format.
691 Major problems cause the program to write a diagnostic to standard error
692 and exit nonzero as usual. The quantity of output varies depending on
693 the verbosity level and whether the plaintext is also being written to
694 standard output. Output lines begin with a keyword:
697 An error prevented decryption. The program will exit nonzero.
701 encountered a situation which may or may not invalidate the decryption.
704 Decryption was successful. This is only produced if main output is
705 being sent somewhere other than standard output.
708 The plaintext follows, starting just after the next newline character or
709 sequence. This is only produced if main output is also being sent to
713 Any other information.
715 The information written at the various verbosity levels is as follows.
717 No output. Watch the exit status.
722 All output written has been checked for authenticity. However, output
723 can fail midway through for many reasons, and the resulting message may
724 therefore be truncated. Don't rely on the output being complete until
732 command encodes an input file according to one of the encodings
735 The input is read from the
737 given on the command line, or from standard input if none is specified.
738 Options provided are:
740 .BI "\-p, \-\-progress"
741 Write a progress meter to standard error while processing large files.
743 .BI "\-f, \-\-format " format
748 for a list of encoding formats.
750 .BI "\-b, \-\-boundary " label
751 Set the PEM boundary string to
753 i.e., assuming we're encoding in PEM format, the output will have
754 .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-"
756 .BI "\-\-\-\-\-END " label "\-\-\-\-\-"
757 at the bottom. The default
762 .BI "\-o, \-\-output " file
765 instead of to standard output.
769 command decodes an input file encoded according to one of the encodings
772 The input is read from the
774 given on the command line, or from standard input if none is specified.
775 Options provided are:
777 .BI "\-f, \-\-format " format
782 for a list of encoding formats.
784 .BI "\-b, \-\-boundary " label
785 Set the PEM boundary string to
787 i.e., assuming we're encoding in PEM format, start processing input
789 .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-"
791 .BI "\-\-\-\-\-END " label "\-\-\-\-\-"
792 lines. Without this option,
794 will start reading at the first plausible boundary string, and continue
795 processing until it reaches the matching end boundary.
797 .BI "\-p, \-\-progress"
798 Write a progress meter to standard error while processing large files.
800 .BI "\-o, \-\-output " file
803 instead of to standard output.
804 .SH "SECURITY PROPERTIES"
805 Assuming the security of the underlying primitive algorithms, the
806 following security properties of the ciphertext hold.
808 An adversary given the public key-encapsulation key and capable of
809 requesting encryption of arbitrary plaintexts of his own devising is
810 unable to decide whether he is given ciphertexts corresponding to his
811 chosen plaintexts or random plaintexts of the same length. This holds
812 even if the adversary is permitted to request decryption of any
813 ciphertext other than one produced as a result of an encryption request.
814 This property is called
817 An adversary given the public key-encapsulation and verification keys,
818 and capable of requesting encryption of arbitrary plaintext of his own
819 devising is unable to produce a new ciphertext which will be accepted as
820 genuine. This property is called
823 An adversary given the public key-encapsulation and verification keys,
824 and capable of requesting encryption of arbitrary plaintext of his own
825 devising is unable to decide whether the ciphertexts he is given are
826 correctly signed. This property doesn't seem to have a name.
828 Not all is rosy. If you leak intermediate values during decryption then
829 an adversary can construct a new correctly-signed message. Don't do
830 that, then \(en leaking intermediate values often voids security
831 warranties. But it does avoid the usual problem with separate signing
832 and encryption that a careful leak by the recipient can produce evidence
833 that you signed some incriminating message.
839 provide `non-repudiation' in any useful way. This is deliberate: the
840 purpose of signing is to convince the recipient of the sender's
841 identity, rather than to allow the recipient to persuade anyone else.
842 Indeed, given an encrypted and signed message, the recipient can
843 straightforwardly construct a new message, apparently from the same
844 sender, and whose signature still verifies, but with arbitrarily chosen
846 .SH "CRYPTOGRAPHIC THEORY"
847 Encryption of a message proceeds as follows.
849 Emit a header packet containing the key-ids for the key-encapsulation
850 key, and signature key if any.
852 Use the KEM to produce a public value and a shared secret the recipient
853 will be able to extract from the public value using his private key.
854 Emit a packet containing the public value.
856 Hash the shared secret. Use the KDF to produce a pseudorandom keystream
857 of indefinite length.
859 Use the first bits of the keystream to key a symmetric encryption
860 scheme; use the next bits to key a message authentication code.
862 If we're signing the message then extract 1024 bytes from the keystream,
863 sign the header and public value, and the keystream bytes; emit a packet
864 containing the signature. The signature packet doesn't contain the
865 signed message, just the signature.
867 Split the message into blocks. For each block, pick a random IV from
868 the keystream, encrypt the block and emit a packet containing the
869 IV, ciphertext, and a MAC tag over the ciphertext and a sequence number.
871 The last chunk is the encryption of an empty plaintext block. No
872 previous plaintext block is empty. This lets us determine the
873 difference between a complete file and one that's been maliciously
876 That's it. Nothing terribly controversial, really.
884 Mark Wooding, <mdw@distorted.org.uk>
~mdw / catacomb / blob