This is the command seccure-dh that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator

**PROGRAM:**

**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-encrypt**ed 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.

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