implemented ECP.hashtopoint() for Coconut

generically useful function, takes any input, hashes with SHA512 and
maps it to a big number to be placed as point on curve. uses milagro's
internal mapit() function which increments big until fitting on curve,
to be enhanced in security by re-hashing.

src/lua/init.lua

@@ -17,11 +17,11 @@ LAMBDA = require('functional')
 L = LAMBDA -- alias
 INSIDE = require('inspect')
 I = INSIDE -- alias
-ECP    = require('ecp')
 ECP2   = require('ecp2')
 FP12   = require('fp12')
 BIG    = require('zenroom_big')
 HASH   = require('zenroom_hash')
+ECP    = require('zenroom_ecp')
 H = HASH -- alias
 
 -- override type to recognize zenroom's types

src/lua/zenroom_ecdh.lua

+local ecdh = require'ecdh'
+
+function prepare_session(keyring, pub) -- internal function
+   local kr
+   if (type(keyring) == "zenroom.ecdh") then
+	  kr = keyring
+   else
+	  error("encrypt error: arg #1 type not known ("..type(keyring)..") expected an ECDH keyring object")
+   end
+   local pk
+   if (type(pub) == "zenroom.ecdh") then
+	  pk = pub:public()
+   elseif (type(pub) == "zenroom.octet") then
+	  pk = pub
+   else
+	  error("encrypt error: arg #2 type not known ("..type(pub)..") expected an ECDH keyring or OCTET object")
+   end
+   return(kr:session(pk))
+end
+
+-- encrypt with default AES-GCM technique, returns base58 encoded
+-- values into a table containing: .text .iv .checksum .header
+function ecdh.encrypt(alice, bob, msg, header)
+   local key = prepare_session(alice,bob)
+   local iv = RNG.new():octet(16)
+   -- convert strings to octets
+   local omsg, ohead
+   if(type(msg) == "string") then
+	  omsg = str(msg) else omsg = msg end
+   if(type(header) == "string") then
+	  ohead = str(header) else ohead = header end
+   local cypher = {header = ohead, iv = iv}
+   cypher.text, cypher.checksum = ecdh.aead_encrypt(key,omsg,iv,ohead)
+   return(cypher)
+end
+
+function ecdh.decrypt(alice, bob, cypher)
+   local key = prepare_session(alice,bob)
+   local decode = {header = cypher.header}
+   decode.text, decode.checksum =
+	  ecdh.aead_decrypt(key,
+				   cypher.text,
+				   cypher.iv,
+				   cypher.header)
+   if(cypher.checksum ~= decode.checksum) then
+	  error("decrypt error: header checksum mismatch")
+   end
+   return(decode)
+end
+
+return ecdh

src/lua/zenroom_ecp.lua

+local ecp = require'ecp'
+
+function ecp.hashtopoint(s) return ecp.mapit(BIG.new(sha512(s))) end
+
+return ecp

src/zen_big.c

@@ -106,8 +106,12 @@ static int newbig(lua_State *L) {
 	// octet argument, import
 	void *ud = luaL_testudata(L, 1, "zenroom.octet");
 	if(ud) {
-		big *c = big_new(L); SAFE(L);
 		octet *o = (octet*)ud;
+		if(o->len < modbytes) {
+			error(L,"Octet too short: %u bytes of %u minimum required",	o->len, modbytes);
+			lerror(L,"Cannot create a BIG number.");
+			return 0; }
+		big *c = big_new(L); SAFE(L);
 		BIG_fromBytesLen(c->val, o->val, o->len);
 		return 1; }
 	// number argument, import
@@ -120,7 +124,7 @@ static int newbig(lua_State *L) {
 		BIG_norm(c->val);
 		return 1; }
 
-	error(L,"octet or number argument expected");
+	lerror(L,"octet or number argument expected");
 	return 0;
 }
 

src/zen_ecp.c

@@ -434,6 +434,7 @@ int luaopen_ecp(lua_State *L) {
 		{"inf",ecp_get_infinity},
 		{"infinity",ecp_get_infinity},
 		{"order",ecp_order},
+		{"mapit",ecp_mapit},
 		{"generator",ecp_generator},
 		{"G",ecp_generator},
 		{NULL,NULL}};
@@ -443,7 +444,6 @@ int luaopen_ecp(lua_State *L) {
 		{"double",ecp_double},
 		{"isinf",ecp_isinf},
 		{"isinfinity",ecp_isinf},
-		{"mapit",ecp_mapit},
 		{"octet",ecp_octet},
 		{"add",ecp_add},
 		{"x",ecp_get_x},