20060303a

1 files changed, 52 insertions, 0 deletions

diff --git a/libsec/port/dsasign.c b/libsec/port/dsasign.c
new file mode 100644
index 00000000..137134be
--- /dev/null
+++ b/libsec/port/dsasign.c
@@ -0,0 +1,52 @@
+#include "os.h"
+#include <mp.h>
+#include <libsec.h>
+
+DSAsig*
+dsasign(DSApriv *priv, mpint *m)
+{
+	DSApub *pub = &priv->pub;
+	DSAsig *sig;
+	mpint *qm1, *k, *kinv, *r, *s;
+	mpint *q = pub->q, *p = pub->p, *alpha = pub->alpha;
+	int qlen = mpsignif(q);
+
+	qm1 = mpnew(0);
+	kinv = mpnew(0);
+	r = mpnew(0);
+	s = mpnew(0);
+	k = mpnew(0);
+	mpsub(pub->q, mpone, qm1);
+
+	// find a k that has an inverse mod q
+	while(1){
+		mprand(qlen, genrandom, k);
+		if((mpcmp(mpone, k) > 0) || (mpcmp(k, pub->q) >= 0))
+			continue;
+		mpextendedgcd(k, q, r, kinv, s);
+		if(mpcmp(r, mpone) != 0)
+			sysfatal("dsasign: pub->q not prime");
+		break;
+	}
+
+  	// make kinv positive
+	mpmod(kinv, pub->q, kinv);
+
+	// r = ((alpha**k) mod p) mod q
+	mpexp(alpha, k, p, r);
+	mpmod(r, q, r);
+
+	// s = (kinv*(m + ar)) mod q
+	mpmul(r, priv->secret, s);
+	mpadd(s, m, s);
+	mpmul(s, kinv, s);
+	mpmod(s, q, s);
+
+	sig = dsasigalloc();
+	sig->r = r;
+	sig->s = s;
+	mpfree(qm1);
+	mpfree(k);
+	mpfree(kinv);
+	return sig;
+}