NAME

       seccure - SECCURE Elliptic Curve Crypto Utility for Reliable Encryption

SYNOPSIS

       seccure-key [-c curve] [-F pwfile] [-d] [-v] [-q]

       seccure-encrypt [-m maclen] [-c curve] [-i infile] [-o outfile] [-v] [-q] key

       seccure-decrypt [-m maclen] [-c curve] [-i infile] [-o outfile] [-F pwfile] [-d] [-v] [-q]

       seccure-sign [-f] [-b] [-a] [-c curve] [-s sigfile] [-i infile] [-o outfile] [-F pwfile] [-d] [-v] [-q]

       seccure-verify [-f] [-b] [-a] [-c curve] [-s sigfile] [-i infile] [-o outfile] [-v] [-q] key [sig]

       seccure-signcrypt [-c sig_curve [-c enc_curve]] [-i infile] [-o outfile] [-F pwfile] [-d] [-v] [-q] key

       seccure-veridec [-c enc_curve [-c sig_curve]] [-i infile] [-o outfile] [-F pwfile] [-d] [-v] [-q] key

       seccure-dh [-c curve] [-v] [-q]

DESCRIPTION

       The  seccure toolset implements a selection of asymmetric algorithms based on elliptic curve cryptography
       (ECC). In particular it offers public key encryption / decryption, signature  generation  /  verification
       and key establishment.

       ECC  schemes  offer  a much better key size to security ratio than classical systems (RSA, DSA). Keys are
       short enough to make direct specification of keys on the command line possible (sometimes  this  is  more
       convenient  than  the  management of PGP-like key rings). seccure builds on this feature and therefore is
       the tool of choice whenever lightweight asymmetric cryptography -- independent of key servers, revocation
       certificates, the Web of Trust or even configuration files -- is required.

COMMANDS

       seccure-key: Prompt for a passphrase and calculate the corresponding public key.

       seccure-encrypt: Encrypt a message with public key key.

       seccure-decrypt: Prompt for a passphrase and decrypt a seccure-encrypted message.

       seccure-sign: Prompt for a passphrase and digitally sign a message.

       seccure-verify: Verify signature sig with public key key.

       seccure-signcrypt:  Sign a message first, encrypt it subsequently (in -b -a and -m 0 mode, respectively).
       This is basically a shortcut for two separate seccure invocations.

       seccure-veridec: Counterpart to signcryption.

       seccure-dh: Perform a Diffie-Hellman key exchange.

OPTIONS

       -c curve
              Use elliptic curve curve. Available  are:  secp112r1,  secp128r1,  secp160r1,  secp192r1/nistp192,
              secp224r1/nistp224,  secp256r1/nistp256, secp384r1/nistp384 and secp521r1/nistp521. The curve name
              may be abbreviated by any non-ambiguous substring (for instance it is suggested  to  specify  p224
              for  the  secp224r1/nistp224 curve). The default curve is p160, which provides reasonable security
              for everyday use. (See also HOW TO CHOOSE THE CURVE.)

              Note: If a public key is given on the command line seccure can determine the  corresponding  curve
              on its own. It's then unnecessary to specify the curve explicitly.

       -F pwfile
              Don't prompt for a passphrase; instead, take the first text line of pwfile.

       -m maclen
              Set the MAC length to maclen bits. Only multiples of 8 in the range from 0 to 256 are allowed. The
              default MAC length is 80 bits, which provides a  reasonable  level  of  integrity  protection  for
              everyday use.

       -i infile
              Read from infile instead of STDIN.

       -o outfile
              Write to outfile instead of STDOUT.

       -s sigfile
              For seccure-sign: Write signature to sigfile instead of STDERR.

              For seccure-verify: Read signature from sigfile instead of using sig.

       -f     Filter mode: Copy all data read from STDIN verbatim to STDOUT (eventually attaching or detaching a
              signature in -a mode).

       -b     Binary mode: Read/write signatures as binary strings. This leads to very compact signatures.

       -a     Append mode:

              For seccure-sign: Append signature to the end of the document. Enforces -f mode.

              For seccure-verify: Detach signature from the end of the document.

       -d     Double prompt mode: When reading a passphrase from  the  console:  prompt  twice  and  assure  the
              phrases are the same.

       -v     Verbose mode: Print some extra information.

       -q     Quiet mode: Disable all unnecessary output.

EXAMPLE

       Given the passphrase 'seccure is secure', run

       seccure-key

       to determine the corresponding public key (which is '2@DupCaCKykHBe-QHpAP%d%B[' on curve p160).

       To encrypt the file 'document.msg' with that key run

       seccure-encrypt -i document.msg -o document.enc '2@DupCaCKykHBe-QHpAP%d%B['

       The message can be recovered with

       seccure-decrypt -i document.enc

       To sign the file run

       seccure-sign -i document.msg -s document.sig

       and enter the passphrase. The signature is stored in 'document.sig' and can be verified with

       seccure-verify -i document.msg -s document.sig '2@DupCaCKykHBe-QHpAP%d%B['

KEY ESTABLISHMENT

       seccure-dh performs an interactive Diffie-Hellman key exchange. Two instances have to be run in parallel;
       the token generated by the first one is the input for the second one and vice versa. The output  consists
       of  two  shared  keys: it is guaranteed that no attacker can ever find out the established key as soon as
       the two parties can confirm that both have the same verification key. The authentic  comparision  of  the
       verification  keys  can,  for  example,  be  realized  via signed messages or via telephone (using 'voice
       authentication').

HOW TO CHOOSE THE CURVE

       The number in the names of the curves measures their security level.  Rule  of  thumb:  the  workload  to
       'break'  a k-bit curve is 2^(k/2) approximately (example: it takes about 2^112 steps to break secp224r1).
       If the 80 bit security of the default curve doesn't seem sufficient, choosing a stronger curve (p192  and
       upwards)  may,  of course, be considered. But the suggestion remains: p160 offers reasonable security for
       everyday use. Warning: the curves p112 and p128 do not satisfy demands for long-time security.

ALGORITHMS

       seccure uses derivated versions of ECIES (Elliptic Curve Integrated Encryption Scheme),  ECDSA  (Elliptic
       Curve  Digital Signature Algorithm) and ECDH (Elliptic Curve Diffie-Hellman) as encryption, signature and
       key  establishment  scheme,  respectively.  For  the  symmetric  parts  (bulk  encryption,  hashing,  key
       derivation,  HMAC  calculation)  seccure  builds  on  AES256 (in CTR mode), SHA256 and SHA512. To my best
       knowledge no part of seccure is covered  by  patents.  See  the  file  PATENTS  for  an  explicit  patent
       statement.

AUTHOR

       This  software  (v0.3)  was  written  by  B. Poettering (seccure AT point-at-infinity.org) in 2006. It is
       released under the terms of the GNU General Public License (GPL). Find the latest version of  seccure  on
       the project's homepage: http://point-at-infinity.org/seccure/.