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/.