1 files changed, 50 insertions, 0 deletions
diff --git a/jni/ed25519/ge_frombytes.c b/jni/ed25519/ge_frombytes.c
new file mode 100644
index 00000000..1a059ee9
--- /dev/null
+++ b/jni/ed25519/ge_frombytes.c
@@ -0,0 +1,50 @@
+#include "ge.h"
+
+static const fe d = {
+#include "d.h"
+} ;
+
+static const fe sqrtm1 = {
+#include "sqrtm1.h"
+} ;
+
+int ge_frombytes_negate_vartime(ge_p3 *h,const unsigned char *s)
+{
+  fe u;
+  fe v;
+  fe v3;
+  fe vxx;
+  fe check;
+
+  fe_frombytes(h->Y,s);
+  fe_1(h->Z);
+  fe_sq(u,h->Y);
+  fe_mul(v,u,d);
+  fe_sub(u,u,h->Z);       /* u = y^2-1 */
+  fe_add(v,v,h->Z);       /* v = dy^2+1 */
+
+  fe_sq(v3,v);
+  fe_mul(v3,v3,v);        /* v3 = v^3 */
+  fe_sq(h->X,v3);
+  fe_mul(h->X,h->X,v);
+  fe_mul(h->X,h->X,u);    /* x = uv^7 */
+
+  fe_pow22523(h->X,h->X); /* x = (uv^7)^((q-5)/8) */
+  fe_mul(h->X,h->X,v3);
+  fe_mul(h->X,h->X,u);    /* x = uv^3(uv^7)^((q-5)/8) */
+
+  fe_sq(vxx,h->X);
+  fe_mul(vxx,vxx,v);
+  fe_sub(check,vxx,u);    /* vx^2-u */
+  if (fe_isnonzero(check)) {
+    fe_add(check,vxx,u);  /* vx^2+u */
+    if (fe_isnonzero(check)) return -1;
+    fe_mul(h->X,h->X,sqrtm1);
+  }
+
+  if (fe_isnegative(h->X) == (s[31] >> 7))
+    fe_neg(h->X,h->X);
+
+  fe_mul(h->T,h->X,h->Y);
+  return 0;
+}