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/.