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 basic key establishment.

       ECC  schemes offer a much better key size to security ratio than classical cryptosystems (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 but nevertheless strong 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, secp521r1/nistp521, brainpoolp160r1,
              brainpoolp192r1,   brainpoolp224r1,   brainpoolp256r1,   brainpoolp320r1,   brainpoolp384r1,   and
              brainpoolp512r1. 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, for all SECP and NIST curves seccure can
              determine the corresponding curve on its  own.  It  is  then  unnecessary  to  specify  the  curve
              explicitly. Brainpool curves cannot be recognized automatically.

       -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. This 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.

EXIT STATUS

       All  commands  in the seccure software suite exit with a status of zero if the desired operation could be
       completed successfully. Any error leads to a nonzero exit code.

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 instance 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  (more  precisely,
       distinguished  from random) 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 name of a curve measures its 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 (v0.5) was written by B. Poettering (seccure AT point-at-infinity.org) in 2006-2014. It  is
       released  under  the  terms of the GNU Lesser General Public License (LGPLv3). Find the latest version of
       seccure on the project's homepage: http://point-at-infinity.org/seccure/.