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.TH ELGAMAL 2
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.SH NAME
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eggen, egencrypt, egdecrypt, egsign, egverify, egpuballoc, egpubfree, egprivalloc, egprivfree, egsigalloc, egsigfree, egprivtopub - elgamal encryption
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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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EGpriv*	eggen(int nlen, int nrep)
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.PP
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.B
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mpint*	egencrypt(EGpub *k, mpint *in, mpint *out)
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.PP
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.B
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mpint*	egdecrypt(EGpriv *k, mpint *in, mpint *out)
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.PP
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.B
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EGsig*	egsign(EGpriv *k, mpint *m)
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.PP
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.B
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int		egverify(EGpub *k, EGsig *sig, mpint *m)
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.PP
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.B
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EGpub*	egpuballoc(void)
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.PP
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.B
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void		egpubfree(EGpub*)
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.PP
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.B
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EGpriv*	egprivalloc(void)
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.PP
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.B
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void		egprivfree(EGpriv*)
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.PP
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.B
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EGsig*	egsigalloc(void)
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.PP
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.B
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void		egsigfree(EGsig*)
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.PP
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.B
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EGpub*	egprivtopub(EGpriv*)
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.SH DESCRIPTION
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.PP
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Elgamal is a public key encryption and signature algorithm.  The owner of a key publishes
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the public part of the key:
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.EX
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	struct EGpub
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	{
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		mpint	*p;	// modulus
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		mpint	*alpha;	// generator
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		mpint	*key;	// (encryption key) alpha**secret mod p
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	};
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.EE
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This part can be used for encrypting data (with
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.IR egencrypt )
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to be sent to the owner.
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The owner decrypts (with
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.IR egdecrypt )
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using his private key:
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.EX
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	struct EGpriv
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	{
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		EGpub	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 eggen .
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.I Eggen
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takes both bit length of the modulus
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and the number of repetitions of the Miller-Rabin
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primality test to run.  If the latter is 0, it does the default number
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of rounds.
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.I Egprivtopub
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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 egpuballoc ,
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.IR egpubfree ,
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.IR egprivalloc ,
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and
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.I egprivfree
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are provided to manage key storage.
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.PP
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.I Egsign
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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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.EX
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	struct EGsig
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	{
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		mpint	*r, *s;
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	};
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.EE
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.I Egverify
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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 egsigalloc
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and
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.I egsigfree
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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 dsa (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)