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 Salsa20 or ChaCha and Poly1305 to secure the bulk data.
261 This is nearly the same as the NaCl
266 uses Salsa20 or ChaCha rather than XSalsa20,
267 because it doesn't need the latter's extended nonce.
270 attribute may be set to one of
281 As well as the KEM itself, a number of supporting algorithms are used.
282 These are taken from appropriately named attributes on the key or,
283 failing that, derived from other attributes as described below.
286 This is the symmetric encryption algorithm
287 used by the bulk data transform.
294 is used; if that it absent, then the default depends on the bulk
298 This is the hash function used to distil entropy from the shared secret
299 constructed by the raw KEM. If there is no
305 is used; if that is absent then the default of
308 .B catcrypt show hash
309 for a list of supported symmetric encryption algorithms.
312 This is the message authentication algorithm
316 to ensure integrity of the encrypted message and
317 defend against chosen-ciphertext attacks.
322 is chosen as a default. Run
324 for a list of supported message authentication algorithms.
327 This is the key derivation function used to stretch the hashed shared
328 secret to a sufficient length to select symmetric encryption and
329 authentication keys, initialization vectors and other necessary
330 pseudorandom quantities. If there is no
334 is chosen as a default. Run
336 for a list of supported key derivation functions.
338 Not all supported functions have the required security features: don't
339 override the default choice unless you know what you're doing.
349 attribute is present on the key, then it must have this form; otherwise,
350 the key's type must have the form
353 Algorithm selections are taken from appropriately-named attributes, or,
354 failing that, from the
357 The signature algorithm is chosen according to the setting of
361 for a list of supported signature algorithms.
364 This is almost the same as the RSASSA-PKCS1-v1_5 algorithm described in
365 RFC3447; the difference is that the hash is left bare rather than being
366 wrapped in a DER-encoded
368 structure. This doesn't affect security since the key can only be used
369 with the one hash function anyway, and dropping the DER wrapping permits
370 rapid adoption of new hash functions. Regardless, use of this algorithm
371 is not recommended, since the padding method has been shown vulnerable
381 This is the RSASSA-PSS algorithm described in RFC3447. It is the
382 preferred RSA-based signature scheme. Use the
391 This is the DSA algorithm described in FIPS180-1 and FIPS180-2. Use the
400 This is the ECDSA algorithm described in ANSI X9.62 and FIPS180-2. Use
410 This is the revised KCDSA (Korean Certificate-based Digital Signature
411 Algorithm) described in
412 .I The Revised Version of KCDSA
413 .RB ( http://dasan.sejong.ac.kr/~chlim/pub/kcdsa1.ps ).
425 This is an unofficial elliptic-curve analogue of the KCDSA algorithm.
435 This is Bernstein, Duif, Lange, Schwabe, and Yang's Ed25519 algorithm.
436 More specifically, this is HashEd25519
439 algorithm \(en by default
451 This is Bernstein, Duif, Lange, Schwabe, and Yang's EdDSA algorithm,
452 using Hamburg's Ed448-Goldilocks elliptic curve,
453 as specified in RFC8032.
454 More specifically, this is HashEd448
457 algorithm \(en by default
469 This uses a symmetric message-authentication algorithm rather than a
470 digital signature. The precise message-authentication scheme used is
473 attribute on the key, which defaults to
475 if unspecified. Use the
483 As well as the signature algorithm itself, a hash function is used.
484 This is taken from the
486 attribute on the key, or, failing that, from the
490 or, if that is absent, determined by the signature algorithm as follows.
498 the default hash function is
505 the default hash function is
509 the default hash function is
513 the default hash function is
517 .B catcrypt show hash
518 for a list of supported hash functions.
520 Two encodings for the ciphertext are supported.
523 The raw format, which has the benefit of being smaller, but needs to be
524 attached to mail messages and generally handled with care.
527 PEM-encapsulated Base-64 encoded text. This format can be included
528 directly in email and picked out again automatically; but there is a
529 4-to-3 data expansion as a result.
530 .SH "COMMAND REFERENCE"
534 command behaves exactly as the
536 option. With no arguments, it shows an overview of
538 options; with arguments, it describes the named subcommands.
542 command prints various lists of tokens understood by
544 With no arguments, it prints all of the lists; with arguments, it prints
545 just the named lists, in order. The recognized lists can be enumerated
550 command. The lists are as follows.
553 The lists which can be enumerated by the
558 The key-encapsulation algorithms which can be used in a
559 key-encapsulation key's
564 The symmetric encryption algorithms which can be used in a
565 key-encapsulation key's
567 attribute when using the
572 The message authentication algorithms which can be used in a
573 key-encapsulation key's
578 The signature algorithms which can be used in a signing key's
583 The hash functions which can be used in a key's
588 The encodings which can be applied to encrypted messages; see
594 command encrypts a file and writes out the appropriately-encoded
595 ciphertext. By default, it reads from standard input and writes to
596 standard output. If a filename argument is given, this file is read
597 instead (as binary data).
599 The following options are recognized.
602 Produce ASCII-armoured output. This is equivalent to specifying
608 .BI "\-f, \-\-format " format
609 Produce output encoded according to
612 .BI "\-k, \-\-key " tag
613 Use the key-encapsulation key named
615 in the current keyring; the default key is
618 .BI "\-p, \-\-progress"
619 Write a progress meter to standard error while processing large files.
621 .BI "\-s, \-\-sign-key " tag
622 Use the signature key named
624 in the current keyring; the default is not to sign the ciphertext.
626 .BI "\-o, \-\-ouptut " file
629 rather than to standard output.
631 .B "\-C, \-\-nocheck"
632 Don't check the public key for validity. This makes encryption go much
633 faster, but at the risk of using a duff key.
637 command decrypts a ciphertext and writes out the plaintext. By default,
638 it reads from standard input and writes to standard output. If a
639 filename argument is given, this file is read instead.
641 The following options are recognized.
644 Read ASCII-armoured input. This is equivalent to specifying
651 Buffer plaintext data until we're sure we've got it all. This is forced
652 on if output is to stdout, but is always available as an option.
654 .BI "\-f, \-\-format " format
655 Read input encoded according to
658 .BI "\-p, \-\-progress"
659 Write a progress meter to standard error while processing large files.
661 .B "\-v, \-\-verbose"
662 Produce more verbose messages. See below for the messages produced
663 during decryption. The default verbosity level is 1. (Currently this
664 is the most verbose setting. This might not be the case always.)
667 Produce fewer messages.
669 .BI "\-o, \-\-output " file
672 instead of to standard output. The file is written in binary mode.
673 Fixing line-end conventions is your problem; there are lots of good
674 tools for dealing with it.
676 .B "\-C, \-\-nocheck"
677 Don't check the private key for validity. This makes decryption go much
678 faster, but at the risk of using a duff key, and possibly leaking
679 information about the private key.
681 Output is written to standard output in a machine-readable format.
682 Major problems cause the program to write a diagnostic to standard error
683 and exit nonzero as usual. The quantity of output varies depending on
684 the verbosity level and whether the plaintext is also being written to
685 standard output. Output lines begin with a keyword:
688 An error prevented decryption. The program will exit nonzero.
692 encountered a situation which may or may not invalidate the decryption.
695 Decryption was successful. This is only produced if main output is
696 being sent somewhere other than standard output.
699 The plaintext follows, starting just after the next newline character or
700 sequence. This is only produced if main output is also being sent to
704 Any other information.
706 The information written at the various verbosity levels is as follows.
708 No output. Watch the exit status.
713 All output written has been checked for authenticity. However, output
714 can fail midway through for many reasons, and the resulting message may
715 therefore be truncated. Don't rely on the output being complete until
723 command encodes an input file according to one of the encodings
726 The input is read from the
728 given on the command line, or from standard input if none is specified.
729 Options provided are:
731 .BI "\-p, \-\-progress"
732 Write a progress meter to standard error while processing large files.
734 .BI "\-f, \-\-format " format
739 for a list of encoding formats.
741 .BI "\-b, \-\-boundary " label
742 Set the PEM boundary string to
744 i.e., assuming we're encoding in PEM format, the output will have
745 .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-"
747 .BI "\-\-\-\-\-END " label "\-\-\-\-\-"
748 at the bottom. The default
753 .BI "\-o, \-\-output " file
756 instead of to standard output.
760 command decodes an input file encoded according to one of the encodings
763 The input is read from the
765 given on the command line, or from standard input if none is specified.
766 Options provided are:
768 .BI "\-f, \-\-format " format
773 for a list of encoding formats.
775 .BI "\-b, \-\-boundary " label
776 Set the PEM boundary string to
778 i.e., assuming we're encoding in PEM format, start processing input
780 .BI "\-\-\-\-\-BEGIN " label "\-\-\-\-\-"
782 .BI "\-\-\-\-\-END " label "\-\-\-\-\-"
783 lines. Without this option,
785 will start reading at the first plausible boundary string, and continue
786 processing until it reaches the matching end boundary.
788 .BI "\-p, \-\-progress"
789 Write a progress meter to standard error while processing large files.
791 .BI "\-o, \-\-output " file
794 instead of to standard output.
795 .SH "SECURITY PROPERTIES"
796 Assuming the security of the underlying primitive algorithms, the
797 following security properties of the ciphertext hold.
799 An adversary given the public key-encapsulation key and capable of
800 requesting encryption of arbitrary plaintexts of his own devising is
801 unable to decide whether he is given ciphertexts corresponding to his
802 chosen plaintexts or random plaintexts of the same length. This holds
803 even if the adversary is permitted to request decryption of any
804 ciphertext other than one produced as a result of an encryption request.
805 This property is called
808 An adversary given the public key-encapsulation and verification keys,
809 and capable of requesting encryption of arbitrary plaintext of his own
810 devising is unable to produce a new ciphertext which will be accepted as
811 genuine. This property is called
814 An adversary given the public key-encapsulation and verification keys,
815 and capable of requesting encryption of arbitrary plaintext of his own
816 devising is unable to decide whether the ciphertexts he is given are
817 correctly signed. This property doesn't seem to have a name.
819 Not all is rosy. If you leak intermediate values during decryption then
820 an adversary can construct a new correctly-signed message. Don't do
821 that, then \(en leaking intermediate values often voids security
822 warranties. But it does avoid the usual problem with separate signing
823 and encryption that a careful leak by the recipient can produce evidence
824 that you signed some incriminating message.
830 provide `non-repudiation' in any useful way. This is deliberate: the
831 purpose of signing is to convince the recipient of the sender's
832 identity, rather than to allow the recipient to persuade anyone else.
833 Indeed, given an encrypted and signed message, the recipient can
834 straightforwardly construct a new message, apparently from the same
835 sender, and whose signature still verifies, but with arbitrarily chosen
837 .SH "CRYPTOGRAPHIC THEORY"
838 Encryption of a message proceeds as follows.
840 Emit a header packet containing the key-ids for the key-encapsulation
841 key, and signature key if any.
843 Use the KEM to produce a public value and a shared secret the recipient
844 will be able to extract from the public value using his private key.
845 Emit a packet containing the public value.
847 Hash the shared secret. Use the KDF to produce a pseudorandom keystream
848 of indefinite length.
850 Use the first bits of the keystream to key a symmetric encryption
851 scheme; use the next bits to key a message authentication code.
853 If we're signing the message then extract 1024 bytes from the keystream,
854 sign the header and public value, and the keystream bytes; emit a packet
855 containing the signature. The signature packet doesn't contain the
856 signed message, just the signature.
858 Split the message into blocks. For each block, pick a random IV from
859 the keystream, encrypt the block and emit a packet containing the
860 IV, ciphertext, and a MAC tag over the ciphertext and a sequence number.
862 The last chunk is the encryption of an empty plaintext block. No
863 previous plaintext block is empty. This lets us determine the
864 difference between a complete file and one that's been maliciously
867 That's it. Nothing terribly controversial, really.
875 Mark Wooding, <mdw@distorted.org.uk>
~mdw / catacomb / blob