Botan 2.19.2
Crypto and TLS for C&
Public Member Functions | Static Public Member Functions | Friends | List of all members
Botan::CT::Mask< T > Class Template Reference

#include <ct_utils.h>

Public Member Functions

T if_not_set_return (T x) const
 
T if_set_return (T x) const
 
void if_set_zero_out (T buf[], size_t elems)
 
bool is_set () const
 
 Mask (const Mask< T > &other)=default
 
template<typename U >
 Mask (Mask< U > o)
 
Mask< T > & operator&= (Mask< T > o)
 
Mask< T > & operator= (const Mask< T > &other)=default
 
Mask< T > & operator^= (Mask< T > o)
 
Mask< T > & operator|= (Mask< T > o)
 
Mask< Toperator~ () const
 
T select (T x, T y) const
 
T select_and_unpoison (T x, T y) const
 
Mask< Tselect_mask (Mask< T > x, Mask< T > y) const
 
void select_n (T output[], const T x[], const T y[], size_t len) const
 
T unpoisoned_value () const
 
T value () const
 

Static Public Member Functions

static Mask< Tcleared ()
 
template<typename U >
static Mask< Texpand (Mask< U > m)
 
static Mask< Texpand (T v)
 
static Mask< Tis_any_of (T v, std::initializer_list< T > accepted)
 
static Mask< Tis_equal (T x, T y)
 
static Mask< Tis_gt (T x, T y)
 
static Mask< Tis_gte (T x, T y)
 
static Mask< Tis_lt (T x, T y)
 
static Mask< Tis_lte (T x, T y)
 
static Mask< Tis_within_range (T v, T l, T u)
 
static Mask< Tis_zero (T x)
 
static Mask< Tset ()
 

Friends

Mask< Toperator& (Mask< T > x, Mask< T > y)
 
Mask< Toperator^ (Mask< T > x, Mask< T > y)
 
Mask< Toperator| (Mask< T > x, Mask< T > y)
 

Detailed Description

template<typename T>
class Botan::CT::Mask< T >

A Mask type used for constant-time operations. A Mask<T> always has value either 0 (all bits cleared) or ~0 (all bits set). All operations in a Mask<T> are intended to compile to code which does not contain conditional jumps. This must be verified with tooling (eg binary disassembly or using valgrind) since you never know what a compiler might do.

Definition at line 87 of file ct_utils.h.

Constructor & Destructor Documentation

◆ Mask() [1/2]

template<typename T >
Botan::CT::Mask< T >::Mask ( const Mask< T > &  other)
default

◆ Mask() [2/2]

template<typename T >
template<typename U >
Botan::CT::Mask< T >::Mask ( Mask< U >  o)
inline

Derive a Mask from a Mask of a larger type

Definition at line 99 of file ct_utils.h.

99 : m_mask(static_cast<T>(o.value()))
100 {
101 static_assert(sizeof(U) > sizeof(T), "sizes ok");
102 }
fe T
Definition: ge.cpp:37

References T.

Member Function Documentation

◆ cleared()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::cleared ( )
inlinestatic

Return a Mask<T> with all bits cleared

Definition at line 115 of file ct_utils.h.

116 {
117 return Mask<T>(0);
118 }

Referenced by Botan::low_zero_bits(), Botan::oaep_find_delim(), Botan::OneAndZeros_Padding::unpad(), and Botan::EME_PKCS1v15::unpad().

◆ expand() [1/2]

template<typename T >
template<typename U >
static Mask< T > Botan::CT::Mask< T >::expand ( Mask< U >  m)
inlinestatic

Return a Mask<T> which is set if m is set

Definition at line 132 of file ct_utils.h.

133 {
134 static_assert(sizeof(U) < sizeof(T), "sizes ok");
135 return ~Mask<T>::is_zero(m.value());
136 }

References T, and Botan::CT::Mask< T >::value().

◆ expand() [2/2]

template<typename T >
static Mask< T > Botan::CT::Mask< T >::expand ( T  v)
inlinestatic

◆ if_not_set_return()

template<typename T >
T Botan::CT::Mask< T >::if_not_set_return ( T  x) const
inline

Return x if the mask is cleared, or otherwise zero

Definition at line 280 of file ct_utils.h.

281 {
282 return ~m_mask & x;
283 }

Referenced by Botan::CT::Mask< T >::if_set_zero_out(), and Botan::EME_PKCS1v15::unpad().

◆ if_set_return()

template<typename T >
T Botan::CT::Mask< T >::if_set_return ( T  x) const
inline

Return x if the mask is set, or otherwise zero

Definition at line 272 of file ct_utils.h.

273 {
274 return m_mask & x;
275 }

Referenced by Botan::oaep_find_delim().

◆ if_set_zero_out()

template<typename T >
void Botan::CT::Mask< T >::if_set_zero_out ( T  buf[],
size_t  elems 
)
inline

If this mask is set, zero out buf, otherwise do nothing

Definition at line 322 of file ct_utils.h.

323 {
324 for(size_t i = 0; i != elems; ++i)
325 {
326 buf[i] = this->if_not_set_return(buf[i]);
327 }
328 }
T if_not_set_return(T x) const
Definition: ct_utils.h:280

References Botan::CT::Mask< T >::if_not_set_return().

Referenced by Botan::CT::copy_output().

◆ is_any_of()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_any_of ( T  v,
std::initializer_list< T accepted 
)
inlinestatic

Definition at line 196 of file ct_utils.h.

197 {
198 T accept = 0;
199
200 for(auto a: accepted)
201 {
202 const T diff = a ^ v;
203 const T eq_zero = ~diff & (diff - 1);
204 accept |= eq_zero;
205 }
206
207 return Mask<T>(expand_top_bit(accept));
208 }
T expand_top_bit(T a)
Definition: bit_ops.h:23

References Botan::expand_top_bit(), and T.

◆ is_equal()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_equal ( T  x,
T  y 
)
inlinestatic

◆ is_gt()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_gt ( T  x,
T  y 
)
inlinestatic

Return a Mask<T> which is set if x > y

Definition at line 165 of file ct_utils.h.

166 {
167 return Mask<T>::is_lt(y, x);
168 }
static Mask< T > is_lt(T x, T y)
Definition: ct_utils.h:157

References Botan::CT::Mask< T >::is_lt().

Referenced by Botan::PKCS7_Padding::unpad(), Botan::ANSI_X923_Padding::unpad(), and Botan::ESP_Padding::unpad().

◆ is_gte()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_gte ( T  x,
T  y 
)
inlinestatic

Return a Mask<T> which is set if x >= y

Definition at line 181 of file ct_utils.h.

182 {
183 return ~Mask<T>::is_lt(x, y);
184 }

Referenced by Botan::ct_divide_u8(), Botan::PKCS7_Padding::unpad(), and Botan::ANSI_X923_Padding::unpad().

◆ is_lt()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_lt ( T  x,
T  y 
)
inlinestatic

Return a Mask<T> which is set if x < y

Definition at line 157 of file ct_utils.h.

158 {
159 return Mask<T>(expand_top_bit<T>(x^((x^y) | ((x-y)^x))));
160 }

Referenced by Botan::bigint_cmp(), Botan::bigint_ct_is_lt(), Botan::TLS::check_tls_cbc_padding(), Botan::CT::Mask< T >::is_gt(), and Botan::Sodium::sodium_compare().

◆ is_lte()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_lte ( T  x,
T  y 
)
inlinestatic

Return a Mask<T> which is set if x <= y

Definition at line 173 of file ct_utils.h.

174 {
175 return ~Mask<T>::is_gt(x, y);
176 }

Referenced by Botan::TLS::check_tls_cbc_padding(), Botan::CT::copy_output(), and Botan::TLS::TLS_CBC_HMAC_AEAD_Decryption::finish().

◆ is_set()

template<typename T >
bool Botan::CT::Mask< T >::is_set ( ) const
inline

Return true iff this mask is set

Definition at line 343 of file ct_utils.h.

344 {
345 return unpoisoned_value() != 0;
346 }
T unpoisoned_value() const
Definition: ct_utils.h:333

References Botan::CT::Mask< T >::unpoisoned_value().

◆ is_within_range()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_within_range ( T  v,
T  l,
T  u 
)
inlinestatic

Definition at line 186 of file ct_utils.h.

187 {
188 //return Mask<T>::is_gte(v, l) & Mask<T>::is_lte(v, u);
189
190 const T v_lt_l = v^((v^l) | ((v-l)^v));
191 const T v_gt_u = u^((u^v) | ((u-v)^u));
192 const T either = v_lt_l | v_gt_u;
193 return ~Mask<T>(expand_top_bit(either));
194 }

References Botan::expand_top_bit(), and T.

◆ is_zero()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::is_zero ( T  x)
inlinestatic

◆ operator&=()

template<typename T >
Mask< T > & Botan::CT::Mask< T >::operator&= ( Mask< T o)
inline

AND-combine two masks

Definition at line 213 of file ct_utils.h.

214 {
215 m_mask &= o.value();
216 return (*this);
217 }

References Botan::CT::Mask< T >::value().

◆ operator=()

template<typename T >
Mask< T > & Botan::CT::Mask< T >::operator= ( const Mask< T > &  other)
default

◆ operator^=()

template<typename T >
Mask< T > & Botan::CT::Mask< T >::operator^= ( Mask< T o)
inline

XOR-combine two masks

Definition at line 222 of file ct_utils.h.

223 {
224 m_mask ^= o.value();
225 return (*this);
226 }

References Botan::CT::Mask< T >::value().

◆ operator|=()

template<typename T >
Mask< T > & Botan::CT::Mask< T >::operator|= ( Mask< T o)
inline

OR-combine two masks

Definition at line 231 of file ct_utils.h.

232 {
233 m_mask |= o.value();
234 return (*this);
235 }

References Botan::CT::Mask< T >::value().

◆ operator~()

template<typename T >
Mask< T > Botan::CT::Mask< T >::operator~ ( ) const
inline

Negate this mask

Definition at line 264 of file ct_utils.h.

265 {
266 return Mask<T>(~value());
267 }
T value() const
Definition: ct_utils.h:351

References Botan::CT::Mask< T >::value().

◆ select()

template<typename T >
T Botan::CT::Mask< T >::select ( T  x,
T  y 
) const
inline

If this mask is set, return x, otherwise return y

Definition at line 288 of file ct_utils.h.

289 {
290 // (x & value()) | (y & ~value())
291 return static_cast<T>(y ^ (value() & (x ^ y)));
292 }

References T, and Botan::CT::Mask< T >::value().

Referenced by Botan::bigint_cnd_add_or_sub(), Botan::bigint_cnd_addsub(), Botan::CT::Mask< T >::select_and_unpoison(), Botan::CT::Mask< T >::select_mask(), and Botan::CT::Mask< T >::select_n().

◆ select_and_unpoison()

template<typename T >
T Botan::CT::Mask< T >::select_and_unpoison ( T  x,
T  y 
) const
inline

Definition at line 294 of file ct_utils.h.

295 {
296 T r = this->select(x, y);
297 CT::unpoison(r);
298 return r;
299 }
T select(T x, T y) const
Definition: ct_utils.h:288
void unpoison(const T *p, size_t n)
Definition: ct_utils.h:59

References Botan::CT::Mask< T >::select(), T, and Botan::CT::unpoison().

◆ select_mask()

template<typename T >
Mask< T > Botan::CT::Mask< T >::select_mask ( Mask< T x,
Mask< T y 
) const
inline

If this mask is set, return x, otherwise return y

Definition at line 304 of file ct_utils.h.

305 {
306 return Mask<T>(select(x.value(), y.value()));
307 }

References Botan::CT::Mask< T >::select(), and Botan::CT::Mask< T >::value().

◆ select_n()

template<typename T >
void Botan::CT::Mask< T >::select_n ( T  output[],
const T  x[],
const T  y[],
size_t  len 
) const
inline

Conditionally set output to x or y, depending on if mask is set or cleared (resp)

Definition at line 313 of file ct_utils.h.

314 {
315 for(size_t i = 0; i != len; ++i)
316 output[i] = this->select(x[i], y[i]);
317 }

References Botan::CT::Mask< T >::select().

◆ set()

template<typename T >
static Mask< T > Botan::CT::Mask< T >::set ( )
inlinestatic

Return a Mask<T> with all bits set

Definition at line 107 of file ct_utils.h.

108 {
109 return Mask<T>(static_cast<T>(~0));
110 }

References T.

Referenced by Botan::oaep_find_delim(), and Botan::CT::strip_leading_zeros().

◆ unpoisoned_value()

template<typename T >
T Botan::CT::Mask< T >::unpoisoned_value ( ) const
inline

Return the value of the mask, unpoisoned

Definition at line 333 of file ct_utils.h.

334 {
335 T r = value();
336 CT::unpoison(r);
337 return r;
338 }

References T, Botan::CT::unpoison(), and Botan::CT::Mask< T >::value().

Referenced by Botan::CT::Mask< T >::is_set().

◆ value()

template<typename T >
T Botan::CT::Mask< T >::value ( ) const
inline

Friends And Related Function Documentation

◆ operator&

template<typename T >
Mask< T > operator& ( Mask< T x,
Mask< T y 
)
friend

AND-combine two masks

Definition at line 240 of file ct_utils.h.

241 {
242 return Mask<T>(x.value() & y.value());
243 }

◆ operator^

template<typename T >
Mask< T > operator^ ( Mask< T x,
Mask< T y 
)
friend

XOR-combine two masks

Definition at line 248 of file ct_utils.h.

249 {
250 return Mask<T>(x.value() ^ y.value());
251 }

◆ operator|

template<typename T >
Mask< T > operator| ( Mask< T x,
Mask< T y 
)
friend

OR-combine two masks

Definition at line 256 of file ct_utils.h.

257 {
258 return Mask<T>(x.value() | y.value());
259 }

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