

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 nonambiguous 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 seccuresign: Write signature to sigfile instead of STDERR.
For seccureverify: 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 seccuresign: Append signature to the end of the document. This enforces f mode. For seccureverify: 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. 
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.
Given the passphrase ’seccure is secure’, runseccurekey
to determine the corresponding public key (which is ’2@DupCaCKykHBeQHpAP%d%B[’ on curve p160).
To encrypt the file ’document.msg’ with that key run
seccureencrypt i document.msg o document.enc ’2@DupCaCKykHBeQHpAP%d%B[’
The message can be recovered with
seccuredecrypt i document.enc
To sign the file run
seccuresign i document.msg s document.sig
and enter the passphrase. The signature is stored in ’document.sig’ and can be verified with
seccureverify i document.msg s document.sig ’2@DupCaCKykHBeQHpAP%d%B[’
seccuredh performs an interactive DiffieHellman 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’).
The number in the name of a curve measures its security level. Rule of thumb: the workload to ’break’ a kbit 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 longtime security.
seccure uses derivated versions of ECIES (Elliptic Curve Integrated Encryption Scheme), ECDSA (Elliptic Curve Digital Signature Algorithm) and ECDH (Elliptic Curve DiffieHellman) 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.
This software (v0.5) was written by B. Poettering (seccure AT pointatinfinity.org) in 20062014. 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://pointatinfinity.org/seccure/.
Manuals  SECCURE (1)  User 
Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.