Botan: Botan::PointGFp Class Reference

Botan 1.10.17

Public Types | Public Member Functions | Friends | List of all members
Botan::PointGFp Class Reference

`#include <point_gfp.h>`

## Public Types
enum | Compression_Type { UNCOMPRESSED = 0, COMPRESSED = 1, HYBRID = 2 }

## Public Member Functions
BigInt | get_affine_x () const
BigInt | get_affine_y () const
const CurveGFp & | get_curve () const
bool | is_zero () const
PointGFp & | negate ()
bool | on_the_curve () const
PointGFp & | operator*= (const BigInt &scalar)
PointGFp & | operator+= (const PointGFp &rhs)
PointGFp & | operator-= (const PointGFp &rhs)
bool | operator== (const PointGFp &other) const
| PointGFp ()
| PointGFp (const CurveGFp &curve)
| PointGFp (const CurveGFp &curve, const BigInt &x, const BigInt &y)
void | swap (PointGFp &other)

## Friends
BOTAN_DLL PointGFp | multi_exponentiate (const PointGFp &p1, const BigInt &z1, const PointGFp &p2, const BigInt &z2)
BOTAN_DLL PointGFp | operator* (const BigInt &scalar, const PointGFp &point)

## Detailed Description

This class represents one point on a curve of GF(p)

Definition at line 41 of file point_gfp.h.

## Member Enumeration Documentation

## ◆ Compression_Type

enum Botan::PointGFp::Compression_Type

Enumerator
UNCOMPRESSED |
COMPRESSED |
HYBRID |

Definition at line 44 of file point_gfp.h.

44 {
45 UNCOMPRESSED = 0,
46 COMPRESSED = 1,
47 HYBRID = 2
48 };
Botan::PointGFp::COMPRESSED
Definition: point_gfp.h:46
Botan::PointGFp::UNCOMPRESSED
Definition: point_gfp.h:45
Botan::PointGFp::HYBRID
Definition: point_gfp.h:47

## Constructor & Destructor Documentation

## ◆ PointGFp() [1/3]

Botan::PointGFp::PointGFp | ( |  | ) |
| inline

Construct an uninitialized PointGFp

Definition at line 53 of file point_gfp.h.

Referenced by operator-=().

53 {}

## ◆ PointGFp() [2/3]

Botan::PointGFp::PointGFp | ( | const CurveGFp & | curve | ) |

Construct the zero point

Parameters

  curve | The base curve

Definition at line 18 of file point_gfp.cpp.

References Botan::CurveGFp::get_r2().

18 :
19 curve(curve), ws(2 * (curve.get_p_words() + 2))
20 {
21 coord_x = 0;
22 coord_y = monty_mult(1, curve.get_r2());
23 coord_z = 0;
24 }
Botan::CurveGFp::get_p_words
size_t get_p_words() const
Definition: curve_gfp.h:89
Botan::CurveGFp::get_r2
const BigInt & get_r2() const
Definition: curve_gfp.h:69

## ◆ PointGFp() [3/3]

Botan::PointGFp::PointGFp | ( | const CurveGFp & | curve,
|  | const BigInt & | x,
|  | const BigInt & | y
| ) |  |

Construct a point from its affine coordinates

Parameters

  curve | the base curve
  x | affine x coordinate
  y | affine y coordinate

Definition at line 26 of file point_gfp.cpp.

References Botan::CurveGFp::get_p(), and Botan::CurveGFp::get_r2().

26 :
27 curve(curve), ws(2 * (curve.get_p_words() + 2))
28 {
29 if(x <= 0 || x >= curve.get_p())
30 throw Invalid_Argument("Invalid PointGFp x");
31 if(y <= 0 || y >= curve.get_p())
32 throw Invalid_Argument("Invalid PointGFp y");
33 coord_x = monty_mult(x, curve.get_r2());
34 coord_y = monty_mult(y, curve.get_r2());
35 coord_z = monty_mult(1, curve.get_r2());
36 }
Botan::CurveGFp::get_p_words
size_t get_p_words() const
Definition: curve_gfp.h:89
Botan::Invalid_Argument
std::invalid_argument Invalid_Argument
Definition: exceptn.h:20
Botan::CurveGFp::get_r2
const BigInt & get_r2() const
Definition: curve_gfp.h:69
Botan::CurveGFp::get_p
const BigInt & get_p() const
Definition: curve_gfp.h:64

## Member Function Documentation

## ◆ get_affine_x()

BigInt Botan::PointGFp::get_affine_x | ( |  | ) | const

get affine x coordinate

Returns
  affine x coordinate

Definition at line 400 of file point_gfp.cpp.

References Botan::CurveGFp::get_p(), Botan::CurveGFp::get_r2(), Botan::inverse_mod(), and is_zero().

Referenced by Botan::ECDH_KA_Operation::agree(), Botan::EC2OSP(), and operator==().

401 {
402 if(is_zero())
403 throw Illegal_Transformation("Cannot convert zero point to affine");
404
405 const BigInt& r2 = curve.get_r2();
406
407 BigInt z2 = monty_sqr(coord_z);
408 z2 = inverse_mod(z2, curve.get_p());
409
410 z2 = monty_mult(z2, r2);
411 return monty_mult(coord_x, z2);
412 }
Botan::inverse_mod
BigInt inverse_mod(const BigInt &n, const BigInt &mod)
Definition: numthry.cpp:314
Botan::CurveGFp::get_r2
const BigInt & get_r2() const
Definition: curve_gfp.h:69
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146
Botan::CurveGFp::get_p
const BigInt & get_p() const
Definition: curve_gfp.h:64

## ◆ get_affine_y()

BigInt Botan::PointGFp::get_affine_y | ( |  | ) | const

get affine y coordinate

Returns
  affine y coordinate

Definition at line 414 of file point_gfp.cpp.

References Botan::CurveGFp::get_p(), Botan::CurveGFp::get_r2(), Botan::inverse_mod(), and is_zero().

Referenced by Botan::EC2OSP(), and operator==().

415 {
416 if(is_zero())
417 throw Illegal_Transformation("Cannot convert zero point to affine");
418
419 const BigInt& r2 = curve.get_r2();
420
421 BigInt z3 = monty_mult(coord_z, monty_sqr(coord_z));
422 z3 = inverse_mod(z3, curve.get_p());
423 z3 = monty_mult(z3, r2);
424 return monty_mult(coord_y, z3);
425 }
Botan::inverse_mod
BigInt inverse_mod(const BigInt &n, const BigInt &mod)
Definition: numthry.cpp:314
Botan::CurveGFp::get_r2
const BigInt & get_r2() const
Definition: curve_gfp.h:69
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146
Botan::CurveGFp::get_p
const BigInt & get_p() const
Definition: curve_gfp.h:64

## ◆ get_curve()

const CurveGFp& Botan::PointGFp::get_curve | ( |  | ) | const
| inline

Return base curve of this point

Returns
  the curve over GF(p) of this point

Definition at line 128 of file point_gfp.h.

Referenced by Botan::EC2OSP(), Botan::operator*(), and operator==().

128 { return curve; }

## ◆ is_zero()

bool Botan::PointGFp::is_zero | ( |  | ) | const
| inline

Is this the point at infinity?

Returns
  true, if this point is at infinity, false otherwise.

Definition at line 146 of file point_gfp.h.

Referenced by Botan::EC2OSP(), get_affine_x(), get_affine_y(), on_the_curve(), operator-=(), and operator==().

147 { return (coord_x.is_zero() && coord_z.is_zero()); }
Botan::BigInt::is_zero
bool is_zero() const
Definition: bigint.h:176

## ◆ negate()

PointGFp& Botan::PointGFp::negate | ( |  | ) |
| inline

Negate this point

Returns
  *this

Definition at line 117 of file point_gfp.h.

References Botan::CT::is_zero().

Referenced by Botan::multi_exponentiate(), Botan::operator*(), and Botan::operator-().

118 {
119 if(!is_zero())
120 coord_y = curve.get_p() - coord_y;
121 return *this;
122 }
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146
Botan::CurveGFp::get_p
const BigInt & get_p() const
Definition: curve_gfp.h:64

## ◆ on_the_curve()

bool Botan::PointGFp::on_the_curve | ( |  | ) | const

Checks whether the point is to be found on the underlying curve; used to prevent fault attacks.

Returns
  if the point is on the curve

Definition at line 427 of file point_gfp.cpp.

References Botan::CurveGFp::get_a_r(), Botan::CurveGFp::get_b_r(), and is_zero().

Referenced by Botan::ECDH_KA_Operation::agree(), Botan::EC_PublicKey::check_key(), Botan::EC_PrivateKey::EC_PrivateKey(), and Botan::OS2ECP().

428 {
429 /*
430 Is the point still on the curve?? (If everything is correct, the
431 point is always on its curve; then the function will return true.
432 If somehow the state is corrupted, which suggests a fault attack
433 (or internal computational error), then return false.
434 */
435
436 if(is_zero())
437 return true;
438
439 BigInt y2 = monty_mult(monty_sqr(coord_y), 1);
440 BigInt x3 = monty_mult(coord_x, monty_sqr(coord_x));
441
442 BigInt ax = monty_mult(coord_x, curve.get_a_r());
443
444 const BigInt& b_r = curve.get_b_r();
445
446 BigInt z2 = monty_sqr(coord_z);
447
448 if(coord_z == z2) // Is z equal to 1 (in Montgomery form)?
449 {
450 if(y2 != monty_mult(x3 + ax + b_r, 1))
451 return false;
452 }
453
454 BigInt z3 = monty_mult(coord_z, z2);
455
456 BigInt ax_z4 = monty_mult(ax, monty_sqr(z2));
457
458 BigInt b_z6 = monty_mult(b_r, monty_sqr(z3));
459
460 if(y2 != monty_mult(x3 + ax_z4 + b_z6, 1))
461 return false;
462
463 return true;
464 }
Botan::CurveGFp::get_b_r
const BigInt & get_b_r() const
Definition: curve_gfp.h:79
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146
Botan::CurveGFp::get_a_r
const BigInt & get_a_r() const
Definition: curve_gfp.h:74

## ◆ operator*=()

PointGFp & Botan::PointGFp::operator*= | ( | const BigInt & | scalar | ) |

*= Operator

Parameters

  scalar | the PointGFp to multiply with *this

Returns
  resulting PointGFp

Definition at line 259 of file point_gfp.cpp.

260 {
261 *this = scalar * *this;
262 return *this;
263 }

## ◆ operator+=()

PointGFp & Botan::PointGFp::operator+= | ( | const PointGFp & | rhs | ) |

+= Operator

Parameters

  rhs | the PointGFp to add to the local value

Returns
  resulting PointGFp

Definition at line 240 of file point_gfp.cpp.

241 {
242 std::vector<BigInt> ws(9);
243 add(rhs, ws);
244 return *this;
245 }

## ◆ operator-=()

PointGFp & Botan::PointGFp::operator-= | ( | const PointGFp & | rhs | ) |

-= Operator

Parameters

  rhs | the PointGFp to subtract from the local value

Returns
  resulting PointGFp

Definition at line 247 of file point_gfp.cpp.

References is_zero(), and PointGFp().

248 {
249 PointGFp minus_rhs = PointGFp(rhs).negate();
250
251 if(is_zero())
252 *this = minus_rhs;
253 else
254 *this += minus_rhs;
255
256 return *this;
257 }
Botan::PointGFp::PointGFp
PointGFp()
Definition: point_gfp.h:53
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146

## ◆ operator==()

bool Botan::PointGFp::operator== | ( | const PointGFp & | other | ) | const

Equality operator

Definition at line 476 of file point_gfp.cpp.

References get_affine_x(), get_affine_y(), get_curve(), and is_zero().

477 {
478 if(get_curve() != other.get_curve())
479 return false;
480
481 // If this is zero, only equal if other is also zero
482 if(is_zero())
483 return other.is_zero();
484
485 return (get_affine_x() == other.get_affine_x() &&
486 get_affine_y() == other.get_affine_y());
487 }
Botan::PointGFp::get_affine_x
BigInt get_affine_x() const
Definition: point_gfp.cpp:400
Botan::PointGFp::get_affine_y
BigInt get_affine_y() const
Definition: point_gfp.cpp:414
Botan::PointGFp::is_zero
bool is_zero() const
Definition: point_gfp.h:146
Botan::PointGFp::get_curve
const CurveGFp & get_curve() const
Definition: point_gfp.h:128

## ◆ swap()

void Botan::PointGFp::swap | ( | PointGFp & | other | ) |

swaps the states of *this and other, does not throw!

Parameters

  other | the object to swap values with

Definition at line 467 of file point_gfp.cpp.

References Botan::CurveGFp::swap(), Botan::MemoryRegion< T >::swap(), and Botan::BigInt::swap().

468 {
469 curve.swap(other.curve);
470 coord_x.swap(other.coord_x);
471 coord_y.swap(other.coord_y);
472 coord_z.swap(other.coord_z);
473 ws.swap(other.ws);
474 }
Botan::BigInt::swap
void swap(BigInt &other)
Definition: bigint.cpp:107
Botan::CurveGFp::swap
void swap(CurveGFp &other)
Definition: curve_gfp.h:95
Botan::MemoryRegion::swap
void swap(MemoryRegion< T > &other)
Definition: secmem.h:260

## Friends And Related Function Documentation

## ◆ multi_exponentiate

BOTAN_DLL PointGFp multi_exponentiate | ( | const PointGFp & | p1,
|  | const BigInt & | z1,
|  | const PointGFp & | p2,
|  | const BigInt & | z2
| ) |  |
| friend

Multiexponentiation

Parameters

  p1 | a point
  z1 | a scalar
  p2 | a point
  z2 | a scalar

Returns
  (p1 * z1 + p2 * z2)

Definition at line 265 of file point_gfp.cpp.

267 {
268 const PointGFp p3 = p1 + p2;
269
270 PointGFp H(p1.curve); // create as zero
271 size_t bits_left = std::max(z1.bits(), z2.bits());
272
273 std::vector<BigInt> ws(9);
274
275 while(bits_left)
276 {
277 H.mult2(ws);
278
279 const bool z1_b = z1.get_bit(bits_left - 1);
280 const bool z2_b = z2.get_bit(bits_left - 1);
281
282 if(z1_b == true && z2_b == true)
283 H.add(p3, ws);
284 else if(z1_b)
285 H.add(p1, ws);
286 else if(z2_b)
287 H.add(p2, ws);
288
289 --bits_left;
290 }
291
292 if(z1.is_negative() != z2.is_negative())
293 H.negate();
294
295 return H;
296 }
Botan::PointGFp::PointGFp
PointGFp()
Definition: point_gfp.h:53
Botan::CT::max
T max(T a, T b)
Definition: ct_utils.h:120

## ◆ operator*

BOTAN_DLL PointGFp operator* | ( | const BigInt & | scalar,
|  | const PointGFp & | point
| ) |  |
| friend

Multiplication Operator

Parameters

  scalar | the scalar value
  point | the point value

Returns
  scalar*point on the curve

Definition at line 298 of file point_gfp.cpp.

299 {
300 const CurveGFp& curve = point.get_curve();
301
302 if(scalar.is_zero())
303 return PointGFp(curve); // zero point
304
305 std::vector<BigInt> ws(9);
306
307 if(scalar.abs() <= 2) // special cases for small values
308 {
309 byte value = scalar.abs().byte_at(0);
310
311 PointGFp result = point;
312
313 if(value == 2)
314 result.mult2(ws);
315
316 if(scalar.is_negative())
317 result.negate();
318
319 return result;
320 }
321
322 const size_t scalar_bits = scalar.bits();
323
324 #if 0
325
326 PointGFp x1 = PointGFp(curve);
327 PointGFp x2 = point;
328
329 size_t bits_left = scalar_bits;
330
331 // Montgomery Ladder
332 while(bits_left)
333 {
334 const bool bit_set = scalar.get_bit(bits_left - 1);
335
336 if(bit_set)
337 {
338 x1.add(x2, ws);
339 x2.mult2(ws);
340 }
341 else
342 {
343 x2.add(x1, ws);
344 x1.mult2(ws);
345 }
346
347 --bits_left;
348 }
349
350 if(scalar.is_negative())
351 x1.negate();
352
353 return x1;
354
355 #else
356 const size_t window_size = 4;
357
358 std::vector<PointGFp> Ps(1 << window_size);
359 Ps[0] = PointGFp(curve);
360 Ps[1] = point;
361
362 for(size_t i = 2; i != Ps.size(); ++i)
363 {
364 Ps[i] = Ps[i-1];
365 Ps[i].add(point, ws);
366 }
367
368 PointGFp H(curve); // create as zero
369 size_t bits_left = scalar_bits;
370
371 while(bits_left >= window_size)
372 {
373 for(size_t i = 0; i != window_size; ++i)
374 H.mult2(ws);
375
376 const u32bit nibble = scalar.get_substring(bits_left - window_size,
377 window_size);
378
379 H.add(Ps[nibble], ws);
380
381 bits_left -= window_size;
382 }
383
384 while(bits_left)
385 {
386 H.mult2(ws);
387 if(scalar.get_bit(bits_left-1))
388 H.add(point, ws);
389
390 --bits_left;
391 }
392
393 if(scalar.is_negative())
394 H.negate();
395
396 return H;
397 #endif
398 }
Botan::byte
unsigned char byte
Definition: types.h:22
Botan::PointGFp::PointGFp
PointGFp()
Definition: point_gfp.h:53
Botan::u32bit
unsigned int u32bit
Definition: types.h:32

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

- src/math/ec_gfp/point_gfp.h
- src/math/ec_gfp/point_gfp.cpp