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<body text="#000000" link="#0000ff" bgcolor="#ffffff"><center><table width="80%">
<tr><td><h1>seccure</h1>
<h2>SECCURE Elliptic Curve Crypto Utility for Reliable Encryption</h2>
<h2>Synopsis</h2>
<b>
seccure-key [-c <em>curve</em>] [-F <em>pwfile</em>] [-d] [-v] [-q]<br>
seccure-encrypt [-m <em>maclen</em>] [-c <em>curve</em>] [-i <em>infile</em>] [-o <em>outfile</em>] [-v] [-q] <em>key</em> <br>
seccure-decrypt [-m <em>maclen</em>] [-c <em>curve</em>] [-i <em>infile</em>] [-o <em>outfile</em>] [-F <em>pwfile</em>] [-d] [-v] [-q] <br>
seccure-sign [-f] [-b] [-a] [-c <em>curve</em>] [-s <em>sigfile</em>] [-i <em>infile</em>] [-o <em>outfile</em>] [-F <em>pwfile</em>] [-d] [-v] [-q] <br>
seccure-verify [-f] [-b] [-a] [-c <em>curve</em>] [-s <em>sigfile</em>] [-i <em>infile</em>] [-o <em>outfile</em>] [-v] [-q] <em>key</em> [<em>sig</em>] <br>
seccure-signcrypt [-c <em>sig_curve</em> [-c <em>enc_curve</em>]] [-i <em>infile</em>] [-o <em>outfile</em>] [-F <em>pwfile</em>] [-d] [-v] [-q] <em>key</em><br>
seccure-veridec [-c <em>enc_curve</em> [-c <em>sig_curve</em>]] [-i <em>infile</em>] [-o <em>outfile</em>] [-F <em>pwfile</em>] [-d] [-v] [-q] <em>key</em><br>
seccure-dh [-c <em>curve</em>] [-v] [-q]<br>
</b>
<h2>Description</h2>
<p>The <b>seccure</b> 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.
</p>
<p>
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).
<b>seccure</b> 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.
</p>
<h2>Commands</h2>
<p><b>seccure-key</b>: Prompt for a passphrase and
calculate the corresponding public key.</p>
<p><b>seccure-encrypt</b>: Encrypt a message with
public key <em>key</em>.</p>
<p><b>seccure-decrypt</b>: Prompt for a passphrase
and decrypt a
<b>seccure-encrypt</b>ed message.</p>
<p><b>seccure-sign</b>: Prompt for a passphrase and
digitally sign a message.</p>
<p><b>seccure-verify</b>: Verify signature <em>sig</em>
with public key <em>key</em>.</p>
<p><b>seccure-signcrypt</b>: Sign a message first, encrypt
it subsequently (in <b>-b -a</b> and <b>-m 0</b> mode,
respectively). This is basically a shortcut for two separate
<b>seccure</b> invocations.</p>
<p><b>seccure-veridec</b>: Counterpart to signcryption.
</p>
<p><b>seccure-dh</b>: Perform a Diffie-Hellman key
exchange.</p>
<h2>Options</h2>
<p><b>-c <em>curve</em></b></p>
<p>Use elliptic curve <em>curve</em>. Available are:
<em>secp112r1</em>, <em>secp128r1</em>, <em>secp160r1</em>,
<em>secp192r1/nistp192</em>, <em>secp224r1/nistp224</em>,
<em>secp256r1/nistp256</em>, <em>secp384r1/nistp384</em> and
<em>secp521r1/nistp521</em>. The curve name may be abbreviated by
any non-ambiguous substring (for instance it is suggested to specify
<em>p224</em> for the <em>secp224r1/nistp224</em> curve). The
default curve is <em>p160</em>, which provides reasonable security
for everyday use. (See also <b>HOW TO CHOOSE THE
CURVE</b>.)</p>
<p>
Note: If a public key is given on the command line
<b>seccure</b> can determine the corresponding curve on its
own. It's then unnecessary to specify the curve explicitly.
</p>
<p><b>-F <em>pwfile</em></b></p>
<p>Don't prompt for a passphrase; instead, take the first text
line of <em>pwfile</em>.</p>
<p><b>-m <em>maclen</em></b></p>
<p>Set the MAC length to <em>maclen</em> 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.</p>
<p><b>-i <em>infile</em></b></p>
<p>
Read from <em>infile</em> instead of STDIN.
</p>
<p><b>-o <em>outfile</em></b></p>
<p>
Write to <em>outfile</em> instead of STDOUT.
</p>
<p><b>-s <em>sigfile</em></b></p>
<p>For <b>seccure-sign</b>: Write signature to
<em>sigfile</em> instead of STDERR. </p>
<p>For <b>seccure-verify</b>: Read signature from
<em>sigfile</em> instead of using <em>sig</em>.
</p>
<p><b>-f</b></p>
<p>Filter mode: Copy all data read from STDIN verbatim to STDOUT
(eventually attaching or detaching a signature in <b>-a</b>
mode).</p>
<p><b>-b</b></p>
<p>Binary mode: Read/write signatures as binary strings. This
leads to very compact signatures.</p>
<p><b>-a</b></p>
<p>Append mode: </p> <p>For <b>seccure-sign</b>: Append
signature to the end of the document. Enforces <b>-f</b>
mode.</p>
<p>For <b>seccure-verify</b>: Detach signature from
the end of the document.
</p>
<p><b>-d</b></p>
<p>Double prompt mode: When reading a passphrase from the console: prompt twice and
assure the phrases are the same.
</p>
<p><b>-v</b></p>
<p>Verbose mode: Print some extra information.</p>
<p><b>-q</b></p>
<p>Quiet mode: Disable all unnecessary output.</p>
<h2>Example</h2>
<p>Given the passphrase 'seccure is secure', run</p>
<p><b>seccure-key</b></p>
<p>to determine the corresponding public key (which is
'2@DupCaCKykHBe-QHpAP%d%B[' on curve <em>p160</em>).</p>
<p>To encrypt the file 'document.msg' with that key run</p>
<p><b>seccure-encrypt -i document.msg -o document.enc '2@DupCaCKykHBe-QHpAP%d%B['</b></p>
<p>The message can be recovered with </p>
<p><b>seccure-decrypt -i document.enc</b></p>
<p>To sign the file run</p>
<p><b>seccure-sign -i document.msg -s document.sig</b></p>
<p>and enter the passphrase. The signature is
stored in 'document.sig' and can be verified with
</p>
<p><b>seccure-verify -i document.msg -s document.sig
'2@DupCaCKykHBe-QHpAP%d%B['</b></p>
<h2>Key establishment</h2>
<b>seccure-dh</b> 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').
<h2>How to choose the curve</h2>
<p>
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
<em>secp224r1</em>). If the 80 bit security of the default curve
doesn't seem sufficient, choosing a stronger curve (<em>p192</em>
and upwards) may, of course, be considered. But the suggestion
remains: <em>p160</em> offers reasonable security for everyday use.
<b>Warning:</b> the curves <em>p112</em> and <em>p128</em> do
not satisfy demands for long-time security.
</p>
<h2>Algorithms</h2>
<p>
<b>seccure</b> 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) <b>seccure</b> builds on AES256 (in CTR mode), SHA256
and SHA512. To my best knowledge no part of <b>seccure</b> is covered
by patents. See the file PATENTS for an explicit patent statement.
</p>
<h2>Author</h2>
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
<b>seccure</b> on the project's homepage: <a href = "http://point-at-infinity.org/seccure/">http://point-at-infinity.org/seccure/</a>.
</td></tr></table></center>
</body>
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