.TH RSA 2
.SH NAME
 - 
.SH SYNOPSIS
.B #include <u.h>
.br
.B #include <libc.h>
.br
.B #include <mp.h>
.br
.B #include <libsec.h>
.PP
.B
RSApriv*	rsagen(int nlen, int elen, int nrep)
.PP
.B
mpint*	rsaencrypt(RSApub *k, mpint *in, mpint *out)
.PP
.B
mpint*	rsadecrypt(RSApriv *k, mpint *in, mpint *out)
.PP
.B
RSApub*	rsapuballoc(void)
.PP
.B
void	rsapubfree(RSApub*)
.PP
.B
RSApriv*	rsaprivalloc(void)
.PP
.B
void	rsaprivfree(RSApriv*)
.PP
.B
RSApub*	rsaprivtopub(RSApriv*)
.PP
.B
RSApub*	X509toRSApub(uchar *cert, int ncert, char *name, int nname)
.PP
.B
RSApriv*	asn1toRSApriv(uchar *priv, int npriv)
.PP
.B
uchar*	decodepem(char *s, char *type, uchar *len)
.SH DESCRIPTION
.PP
RSA is a public key encryption algorithm.  The owner of a key publishes
the public part of the key:
.EX
	struct RSApub
	{
		mpint	*n;	// modulus
		mpint	*ek;	// exp (encryption key)
	};
.EE
This part can be used for encrypting data (with
.IR rsaencrypt )
to be sent to the owner.
The owner decrypts (with
.IR rsadecrypt )
using his private key:
.EX
	struct RSApriv
	{
		RSApub	pub;
		mpint	*dk;	// exp (decryption key)
	
		// precomputed crt values
		mpint	*p;
		mpint	*q;
		mpint	*kp;	// k mod p-1
		mpint	*kq;	// k mod q-1
		mpint	*c2;	// for converting residues to number
	};
.EE
.PP
Keys are generated using
.IR rsagen .
.I Rsagen
takes both bit length of the modulus, the bit length of the
public key exponent, and the number of repetitions of the Miller-Rabin
primality test to run.  If the latter is 0, it does the default number
of rounds.
.I Rsagen
returns a newly allocated structure containing both
public and private keys.
.I Rsaprivtopub
returns a newly allocated copy of the public key
corresponding to the private key.
.PP
The routines
.IR rsaalloc ,
.IR rsafree ,
.IR rsapuballoc ,
.IR rsapubfree ,
.IR rsaprivalloc ,
and
.I rsaprivfree
are provided to aid in user provided key I/O.
.PP
Given a binary X.509
.IR cert ,
the routine
.I X509toRSApub
returns the public key and, if
.I name
is not nil, the CN part of the Distinguished Name of the
certificate's Subject.
(This is conventionally a userid or a host DNS name.)
No verification is done of the certificate signature;  the
caller should check the fingerprint,
.IR sha1(cert) ,
against a table or check the certificate by other means.
X.509 certificates are often stored in PEM format; use
.I dec64
to convert to binary before computing the fingerprint or calling
.IR X509toRSApub .
.PP
.I Asn1toRSApriv
converts an ASN1 formatted RSA private key into the corresponding
.B RSApriv
structure.
.PP
.I Decodepem
takes a zero terminated string,
.IR s ,
and decodes the PEM (privacy-enhanced mail) formatted section for
.I type
within it.
If successful, it returns the decoded section and sets
.BI * len
to its decoded length.
If not, it returns
.BR nil ,
and
.BI * len
is undefined.
.SH SOURCE
.B /sys/src/libsec
.SH SEE ALSO
.IR mp (2),
.IR aes (2),
.IR blowfish (2),
.IR des (2),
.IR elgamal (2),
.IR rc4 (2),
.IR sechash (2),
.IR prime (2),
.IR rand (2)