Element of prime-order elliptic curve group. More...

#include <point_255.hxx>

Inheritance diagram for decaf::Ristretto::Point:

Public Types
typedef decaf_255_point_t	Wrapped
	Wrapped C type.

Public Member Functions
	Point (const Wrapped &q=decaf_255_point_identity) DECAF_NOEXCEPT
	Constructor sets to identity by default.

	Point (const Point &q) DECAF_NOEXCEPT
	Copy constructor.

Point &	operator= (const Point &q) DECAF_NOEXCEPT
	Assignment.

	~Point () DECAF_NOEXCEPT
	Destructor securely zeorizes the point.

	Point (Rng &rng, bool uniform=true) DECAF_NOEXCEPT
	Construct from RNG.

	Point (const FixedBlock< SER_BYTES > &buffer, bool allow_identity=true)
	Initialize from a fixed-length byte string.

decaf_error_t DECAF_WARN_UNUSED	decode (const FixedBlock< SER_BYTES > &buffer, bool allow_identity=true) DECAF_NOEXCEPT
	Initialize from C++ fixed-length byte string.

decaf_error_t DECAF_WARN_UNUSED	decode_like_eddsa_and_mul_by_ratio_noexcept (const FixedBlock< DECAF_EDDSA_25519_PUBLIC_BYTES > &buffer) DECAF_NOEXCEPT
	Initialize from C++ fixed-length byte string, like EdDSA.

void	decode_like_eddsa_and_mul_by_ratio (const FixedBlock< DECAF_EDDSA_25519_PUBLIC_BYTES > &buffer)
	Decode from EDDSA, multiply by EDDSA_DECODE_RATIO, and ignore any remaining cofactor information.

SecureBuffer	mul_by_ratio_and_encode_like_eddsa () const
	Multiply by EDDSA_ENCODE_RATIO and encode like EdDSA.

void	mul_by_ratio_and_encode_like_eddsa (FixedBuffer< DECAF_EDDSA_25519_PUBLIC_BYTES > &out) const
	Multiply by EDDSA_ENCODE_RATIO and encode like EdDSA.

SecureBuffer	mul_by_ratio_and_encode_like_ladder () const
	Multiply by LADDER_ENCODE_RATIO and encode like X25519/X448.

void	mul_by_ratio_and_encode_like_ladder (FixedBuffer< LADDER_BYTES > &out) const
	Multiply by LADDER_ENCODE_RATIO and encode like X25519/X448.

void	set_to_hash (const Block &s) DECAF_NOEXCEPT
	Map to the curve from a hash buffer.

	operator SecureBuffer () const
	Encode to string.

size_t	ser_size () const DECAF_NOEXCEPT
	Serializable instance.

void	serialize_into (unsigned char *buffer) const DECAF_NOEXCEPT
	Serializable instance.

Point	operator+ (const Point &q) const DECAF_NOEXCEPT
	Point add.

Point &	operator+= (const Point &q) DECAF_NOEXCEPT
	Point add.

Point	operator- (const Point &q) const DECAF_NOEXCEPT
	Point subtract.

Point &	operator-= (const Point &q) DECAF_NOEXCEPT
	Point subtract.

Point	operator- () const DECAF_NOEXCEPT
	Point negate.

Point	times_two () const DECAF_NOEXCEPT
	Double the point out of place.

Point &	double_in_place () DECAF_NOEXCEPT
	Double the point in place.

bool	operator!= (const Point &q) const DECAF_NOEXCEPT
	Constant-time compare.

bool	operator== (const Point &q) const DECAF_NOEXCEPT
	Constant-time compare.

Point	operator* (const Scalar &s) const DECAF_NOEXCEPT
	Scalar multiply.

Point &	*operator=** (const Scalar &s) DECAF_NOEXCEPT
	Scalar multiply in place.

Point	operator/ (const Scalar &s) const
	Multiply by s.inverse().

Point &	operator/= (const Scalar &s)
	Multiply by s.inverse().

bool	validate () const DECAF_NOEXCEPT
	Validate / sanity check.

void	dual_scalarmul (Point &q1, Point &q2, const Scalar &r1, const Scalar &r2) const DECAF_NOEXCEPT
	Dual-scalar multiply, equivalent to thisr1, thisr2 but faster.

Point	non_secret_combo_with_base (const Scalar &s, const Scalar &s_base) DECAF_NOEXCEPT
	Double-scalar multiply: this point by the first scalar and base by the second scalar.

Point	debugging_torque () const DECAF_NOEXCEPT
	Return a point equal to *this, whose internal data is rotated by a torsion element.

Point	debugging_pscale (const FixedBlock< SER_BYTES > factor) const DECAF_NOEXCEPT
	Return a point equal to *this, whose internal data has a modified representation.

Point	debugging_pscale (Rng &r) const DECAF_NOEXCEPT
	Return a point equal to *this, whose internal data has a randomized representation.

decaf_error_t	invert_elligator (Buffer buf, uint32_t hint) const DECAF_NOEXCEPT
	Modify buffer so that Point::from_hash(Buffer) == *this, and return DECAF_SUCCESS; or leave buf unmodified and return DECAF_FAILURE.

SecureBuffer	steg_encode (Rng &rng) const
	Steganographically encode this.

Public Member Functions inherited from decaf::Serializable< Point >
size_t	ser_size () const DECAF_NOEXCEPT
	Return the number of bytes needed to serialize this object.

void	serialize_into (unsigned char *buf) const DECAF_NOEXCEPT
	Serialize this object into a buffer.

SecureBuffer	serialize () const
	Serialize this object into a SecureBuffer and return it.

Static Public Member Functions
static Point	from_hash (const Block &s) DECAF_NOEXCEPT
	Map uniformly to the curve from a hash buffer.

static Point	double_scalarmul (const Point &q, const Scalar &qs, const Point &r, const Scalar &rs) DECAF_NOEXCEPT
	Double-scalar multiply, equivalent to qqs + rrs but faster.

static Point	double_scalarmul (const Scalar &qs, const Point &q, const Scalar &rs, const Point &r) DECAF_NOEXCEPT
	Double-scalar multiply, equivalent to qqs + rrs but faster.

static const Point	base () DECAF_NOEXCEPT
	Return the base point of the curve.

static const Point	identity () DECAF_NOEXCEPT
	Return the identity point of the curve.

Public Attributes
Wrapped	p
	The c-level object.

Static Public Attributes
static const size_t	SER_BYTES = DECAF_255_SER_BYTES
	Size of a serialized element.

static const size_t	HASH_BYTES = DECAF_255_HASH_BYTES
	Bytes required for hash.

static const size_t	EDDSA_BYTES = DECAF_EDDSA_25519_PUBLIC_BYTES
	Bytes required for EdDSA encoding.

static const size_t	LADDER_BYTES = DECAF_X25519_PUBLIC_BYTES
	Bytes required for EdDSA encoding.

static const int	EDDSA_ENCODE_RATIO = DECAF_255_EDDSA_ENCODE_RATIO
	Ratio due to EdDSA encoding.

static const int	EDDSA_DECODE_RATIO = DECAF_255_EDDSA_DECODE_RATIO
	Ratio due to EdDSA decoding.

static const int	LADDER_ENCODE_RATIO = DECAF_X25519_ENCODE_RATIO
	Ratio due to ladder decoding.

static const size_t	STEG_BYTES = HASH_BYTES * 2
	Size of a steganographically-encoded curve element.

static const unsigned int	INVERT_ELLIGATOR_WHICH_BITS = DECAF_255_INVERT_ELLIGATOR_WHICH_BITS
	Number of bits in invert_elligator which are actually used.

Detailed Description

Element of prime-order elliptic curve group.

Constructor & Destructor Documentation

◆ Point()

decaf::Ristretto::Point::Point	(	const FixedBlock< SER_BYTES > &	buffer,
		bool	allow_identity = `true`
	)

inlineexplicit

Initialize from a fixed-length byte string.

The all-zero string maps to the identity.

Exceptions

CryptoException the string was the wrong length, or wasn't the encoding of a point, or was the identity and allow_identity was DECAF_FALSE.

Member Function Documentation

◆ decode()

decaf_error_t DECAF_WARN_UNUSED decaf::Ristretto::Point::decode	(	const FixedBlock< SER_BYTES > &	buffer,
		bool	allow_identity = `true`
	)

inline

Initialize from C++ fixed-length byte string.

The all-zero string maps to the identity.

Return values

DECAF_SUCCESS the string was successfully decoded.

Returns: DECAF_FAILURE the string was the wrong length, or wasn't the encoding of a point, or was the identity and allow_identity was DECAF_FALSE. Contents of the buffer are undefined.

◆ decode_like_eddsa_and_mul_by_ratio()

void decaf::Ristretto::Point::decode_like_eddsa_and_mul_by_ratio ( const FixedBlock< DECAF_EDDSA_25519_PUBLIC_BYTES > & buffer )

inline

Decode from EDDSA, multiply by EDDSA_DECODE_RATIO, and ignore any remaining cofactor information.

Exceptions

CryptoException if the input point was invalid.

◆ decode_like_eddsa_and_mul_by_ratio_noexcept()

decaf_error_t DECAF_WARN_UNUSED decaf::Ristretto::Point::decode_like_eddsa_and_mul_by_ratio_noexcept ( const FixedBlock< DECAF_EDDSA_25519_PUBLIC_BYTES > & buffer )

inline

Initialize from C++ fixed-length byte string, like EdDSA.

The all-zero string maps to the identity.

Return values

DECAF_SUCCESS the string was successfully decoded.

Returns: DECAF_FAILURE the string was the wrong length, or wasn't the encoding of a point. Contents of the point are undefined.

◆ double_scalarmul()

static Point decaf::Ristretto::Point::double_scalarmul	(	const Scalar &	qs,
		const Point &	q,
		const Scalar &	rs,
		const Point &	r
	)

inlinestatic

Double-scalar multiply, equivalent to q*qs + r*rs but faster.

For those who like their scalars before the point.

◆ from_hash()

static Point decaf::Ristretto::Point::from_hash ( const Block & s )

inlinestatic

Map uniformly to the curve from a hash buffer.

The empty or all-zero string maps to the identity, as does the string "\\x01". If the buffer is shorter than 2*HASH_BYTES, well, it won't be as uniform, but the buffer will be zero-padded on the right.

◆ non_secret_combo_with_base()

Point decaf::Ristretto::Point::non_secret_combo_with_base	(	const Scalar &	s,
		const Scalar &	s_base
	)

inline

Double-scalar multiply: this point by the first scalar and base by the second scalar.

Warning: This function takes variable time, and may leak the scalars (or points, but currently it doesn't).

◆ operator SecureBuffer()

decaf::Ristretto::Point::operator SecureBuffer ( ) const

inline

Encode to string.

The identity encodes to the all-zero string.

◆ operator/()

Point decaf::Ristretto::Point::operator/ ( const Scalar & s ) const

inline

Multiply by s.inverse().

If s=0, maps to the identity.

◆ operator/=()

Point & decaf::Ristretto::Point::operator/= ( const Scalar & s )

inline

Multiply by s.inverse().

If s=0, maps to the identity.

◆ set_to_hash()

void decaf::Ristretto::Point::set_to_hash ( const Block & s )

inline

Map to the curve from a hash buffer.

The empty or all-zero string maps to the identity, as does the string "\\x01". If the buffer is shorter than 2*HASH_BYTES, well, it won't be as uniform, but the buffer will be zero-padded on the right.

Member Data Documentation

◆ STEG_BYTES

const size_t decaf::Ristretto::Point::STEG_BYTES = HASH_BYTES * 2

static

Size of a steganographically-encoded curve element.

If the point is random, the encoding should look statistically close to a uniformly-random sequnece of STEG_BYTES bytes.

The documentation for this class was generated from the following file:

src/GENERATED/include/decaf/point_255.hxx

Public Types

Public Member Functions

Static Public Member Functions

Public Attributes

Static Public Attributes

Detailed Description

Constructor & Destructor Documentation

◆ Point()

Member Function Documentation

◆ decode()

◆ decode_like_eddsa_and_mul_by_ratio()

◆ decode_like_eddsa_and_mul_by_ratio_noexcept()

◆ double_scalarmul()

◆ from_hash()

◆ non_secret_combo_with_base()

◆ operator SecureBuffer()

◆ operator/()

◆ operator/=()

◆ set_to_hash()

Member Data Documentation

◆ STEG_BYTES