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.TH DSA 2
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.SH NAME
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dsagen, dsasign, dsaverify, dsapuballoc, dsapubfree, dsaprivalloc, dsaprivfree, dsasigalloc, dsasigfree, dsaprivtopub - digital signature algorithm
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.br
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.B #include <mp.h>
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.br
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.B #include <libsec.h>
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.PP
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.B
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DSApriv*	dsagen(DSApub *opub)
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.PP
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.B
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DSAsig*	dsasign(DSApriv *k, mpint *m)
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.PP
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.B
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int		dsaverify(DSApub *k, DSAsig *sig, mpint *m)
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.PP
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.B
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DSApub*	dsapuballoc(void)
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.PP
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.B
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void		dsapubfree(DSApub*)
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.PP
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.B
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DSApriv*	dsaprivalloc(void)
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.PP
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.B
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void		dsaprivfree(DSApriv*)
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.PP
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.B
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DSAsig*	dsasigalloc(void)
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.PP
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.B
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void		dsasigfree(DSAsig*)
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.PP
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.B
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DSApub*	dsaprivtopub(DSApriv*)
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.SH DESCRIPTION
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.PP
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DSA is the NIST approved digital signature algorithm.  The owner of a key publishes
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the public part of the key:
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.IP
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.EX
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struct DSApub
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{
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	mpint	*p;	// modulus
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	mpint	*q;	// group order, q divides p-1
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	mpint	*alpha;	// group generator
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	mpint	*key;	// alpha**secret mod p
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};
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.EE
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.LP
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This part can be used for verifying signatures (with
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.IR dsaverify )
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created by the owner.
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The owner signs (with
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.IR dsasign )
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using his private key:
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.IP
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.EX
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struct DSApriv
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{
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	DSApub	pub;
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	mpint	*secret; // (decryption key)
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};
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.EE
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.PP
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Keys are generated using
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.IR dsagen .
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If
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.IR dsagen 's
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argument
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.I opub
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is
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.BR nil ,
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a key is created using a new
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.B p
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and
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.B q
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generated by
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.I DSAprimes
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(see
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.IR prime (2)).
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Otherwise,
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.B p
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and
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.B q
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are copied from the old key.
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.PP
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.I Dsaprivtopub
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returns a newly allocated copy of the public key
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corresponding to the private key.
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.PP
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The routines
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.IR dsapuballoc ,
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.IR dsapubfree ,
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.IR dsaprivalloc ,
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and
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.I dsaprivfree
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are provided to manage key storage.
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.PP
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.I Dsasign
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signs message
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.I m
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using a private key
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.I k
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yielding a
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.IP
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.EX
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struct DSAsig
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{
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	mpint	*r, *s;
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};
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.EE
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.LP
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.I Dsaverify
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returns 0 if the signature is valid and \-1 if not.
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.PP
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The routines
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.I dsasigalloc
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and
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.I dsasigfree
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are provided to manage signature storage.
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.SH SOURCE
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.B /sys/src/libsec
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.SH SEE ALSO
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.IR mp (2),
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.IR aes (2),
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.IR blowfish (2),
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.IR des (2),
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.IR rc4 (2),
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.IR rsa (2),
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.IR sechash (2),
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.IR prime (2),
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.IR rand (2),
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.IR dsa (8)