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/*
* ECC Domain Parameters
*
* (C) 2007 Falko Strenzke, FlexSecure GmbH
* 2008 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ec_group.h>
#include <botan/ber_dec.h>
#include <botan/der_enc.h>
#include <botan/oids.h>
#include <botan/pem.h>
#include <botan/reducer.h>
namespace Botan {
EC_Group::EC_Group(const OID& domain_oid)
{
const std::string pem = PEM_for_named_group(OIDS::lookup(domain_oid));
if(pem == "")
{
throw Lookup_Error("No ECC domain data for '" + domain_oid.as_string() + "'");
}
*this = EC_Group(pem);
m_oid = domain_oid.as_string();
}
EC_Group::EC_Group(const std::string& str)
{
if(str == "")
return; // no initialization / uninitialized
try
{
std::vector<uint8_t> ber =
unlock(PEM_Code::decode_check_label(str, "EC PARAMETERS"));
*this = EC_Group(ber);
}
catch(Decoding_Error) // hmm, not PEM?
{
*this = EC_Group(OIDS::lookup(str));
}
}
EC_Group::EC_Group(const std::vector<uint8_t>& ber_data)
{
BER_Decoder ber(ber_data);
BER_Object obj = ber.get_next_object();
if(obj.type() == NULL_TAG)
throw Decoding_Error("Cannot handle ImplicitCA ECDSA parameters");
else if(obj.type() == OBJECT_ID)
{
OID dom_par_oid;
BER_Decoder(ber_data).decode(dom_par_oid);
*this = EC_Group(dom_par_oid);
}
else if(obj.type() == SEQUENCE)
{
BigInt p, a, b;
std::vector<uint8_t> sv_base_point;
BER_Decoder(ber_data)
.start_cons(SEQUENCE)
.decode_and_check<size_t>(1, "Unknown ECC param version code")
.start_cons(SEQUENCE)
.decode_and_check(OID("1.2.840.10045.1.1"),
"Only prime ECC fields supported")
.decode(p)
.end_cons()
.start_cons(SEQUENCE)
.decode_octet_string_bigint(a)
.decode_octet_string_bigint(b)
.end_cons()
.decode(sv_base_point, OCTET_STRING)
.decode(m_order)
.decode(m_cofactor)
.end_cons()
.verify_end();
m_curve = CurveGFp(p, a, b);
m_base_point = OS2ECP(sv_base_point, m_curve);
}
else
throw Decoding_Error("Unexpected tag while decoding ECC domain params");
}
std::vector<uint8_t>
EC_Group::DER_encode(EC_Group_Encoding form) const
{
if(form == EC_DOMPAR_ENC_EXPLICIT)
{
const size_t ecpVers1 = 1;
OID curve_type("1.2.840.10045.1.1");
const size_t p_bytes = m_curve.get_p().bytes();
return DER_Encoder()
.start_cons(SEQUENCE)
.encode(ecpVers1)
.start_cons(SEQUENCE)
.encode(curve_type)
.encode(m_curve.get_p())
.end_cons()
.start_cons(SEQUENCE)
.encode(BigInt::encode_1363(m_curve.get_a(), p_bytes),
OCTET_STRING)
.encode(BigInt::encode_1363(m_curve.get_b(), p_bytes),
OCTET_STRING)
.end_cons()
.encode(EC2OSP(m_base_point, PointGFp::UNCOMPRESSED), OCTET_STRING)
.encode(m_order)
.encode(m_cofactor)
.end_cons()
.get_contents_unlocked();
}
else if(form == EC_DOMPAR_ENC_OID)
{
if(get_oid().empty())
{
throw Encoding_Error("Cannot encode EC_Group as OID because OID not set");
}
return DER_Encoder().encode(OID(get_oid())).get_contents_unlocked();
}
else if(form == EC_DOMPAR_ENC_IMPLICITCA)
return DER_Encoder().encode_null().get_contents_unlocked();
else
throw Internal_Error("EC_Group::DER_encode: Unknown encoding");
}
std::string EC_Group::PEM_encode() const
{
const std::vector<uint8_t> der = DER_encode(EC_DOMPAR_ENC_EXPLICIT);
return PEM_Code::encode(der, "EC PARAMETERS");
}
bool EC_Group::verify_group(RandomNumberGenerator& rng,
bool) const
{
//compute the discriminant
Modular_Reducer p(m_curve.get_p());
BigInt discriminant = p.multiply(4, m_curve.get_a());
discriminant += p.multiply(27, m_curve.get_b());
discriminant = p.reduce(discriminant);
//check the discriminant
if(discriminant == 0)
{
return false;
}
//check for valid cofactor
if(m_cofactor < 1)
{
return false;
}
//check if the base point is on the curve
if(!m_base_point.on_the_curve())
{
return false;
}
if((m_base_point * m_cofactor).is_zero())
{
return false;
}
//check if order is prime
if(!is_prime(m_order, rng, 128))
{
return false;
}
//check if order of the base point is correct
if(!(m_base_point * m_order).is_zero())
{
return false;
}
return true;
}
}
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