Botan 3.1.1
Crypto and TLS for C&
Public Member Functions | Static Public Member Functions | Friends | List of all members
Botan::CT::Mask< T > Class Template Referencefinal

#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< T > operator~ () const
 
T select (T x, T y) const
 
T select_and_unpoison (T x, T y) const
 
Mask< T > select_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< T > cleared ()
 
template<typename U >
static Mask< T > expand (Mask< U > m)
 
static Mask< T > expand (T v)
 
static Mask< T > is_any_of (T v, std::initializer_list< T > accepted)
 
static Mask< T > is_equal (T x, T y)
 
static Mask< T > is_gt (T x, T y)
 
static Mask< T > is_gte (T x, T y)
 
static Mask< T > is_lt (T x, T y)
 
static Mask< T > is_lte (T x, T y)
 
static Mask< T > is_within_range (T v, T l, T u)
 
static Mask< T > is_zero (T x)
 
static Mask< T > set ()
 

Friends

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

Detailed Description

template<typename T>
requires std::is_unsigned<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 83 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 92 of file ct_utils.h.

92 : m_mask(static_cast<T>(o.value())) {
93 static_assert(sizeof(U) > sizeof(T), "sizes ok");
94 }
T
FE_25519 T
Definition: ge.cpp:34

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 104 of file ct_utils.h.

104{ return Mask<T>(0); }

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 115 of file ct_utils.h.

115 {
116 static_assert(sizeof(U) < sizeof(T), "sizes ok");
117 return ~Mask<T>::is_zero(m.value());
118 }

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

Return a Mask<T> which is set if v is != 0

Definition at line 109 of file ct_utils.h.

109{ return ~Mask<T>::is_zero(v); }

Referenced by Botan::bigint_cnd_abs(), Botan::bigint_cnd_add(), Botan::bigint_cnd_sub(), Botan::bigint_cnd_swap(), Botan::bigint_ct_is_lt(), Botan::bigint_shl1(), Botan::bigint_shl2(), Botan::bigint_shr1(), Botan::bigint_shr2(), Botan::BigInt::cond_flip_sign(), Botan::CT::conditional_assign_mem(), Botan::CT::conditional_copy_mem(), Botan::CT::conditional_swap(), Botan::CT::copy_output(), Botan::BigInt::ct_cond_assign(), Botan::ct_divide_word(), Botan::gcd(), Botan::low_zero_bits(), Botan::redc_p521(), Botan::Sodium::sodium_is_zero(), Botan::ANSI_X923_Padding::unpad(), and Botan::OneAndZeros_Padding::unpad().

◆ 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 223 of file ct_utils.h.

223{ return ~m_mask & x; }

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 218 of file ct_utils.h.

218{ return m_mask & x; }

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 253 of file ct_utils.h.

253 {
254 for(size_t i = 0; i != elems; ++i) {
255 buf[i] = this->if_not_set_return(buf[i]);
256 }
257 }
Botan::CT::Mask::if_not_set_return
T if_not_set_return(T x) const
Definition: ct_utils.h:223

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

◆ 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 159 of file ct_utils.h.

159 {
160 T accept = 0;
161
162 for(auto a : accepted) {
163 const T diff = a ^ v;
164 const T eq_zero = ~diff & (diff - 1);
165 accept |= eq_zero;
166 }
167
168 return Mask<T>(expand_top_bit(accept));
169 }
Botan::expand_top_bit
constexpr 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

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

Definition at line 128 of file ct_utils.h.

128{ return Mask<T>::is_zero(static_cast<T>(x ^ y)); }
Botan::CT::Mask::is_zero
static Mask< T > is_zero(T x)
Definition: ct_utils.h:123

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

Referenced by Botan::bigint_cmp(), Botan::bigint_ct_is_lt(), Botan::TLS::check_tls_cbc_padding(), Botan::CT::copy_output(), Botan::PK_Decryptor::decrypt_or_random(), Botan::EC_Point_Base_Point_Precompute::mul(), Botan::EC_Point_Var_Point_Precompute::mul(), Botan::oaep_find_delim(), Botan::redc_p521(), Botan::Sodium::sodium_compare(), Botan::PKCS7_Padding::unpad(), Botan::OneAndZeros_Padding::unpad(), Botan::ESP_Padding::unpad(), and Botan::vartime_divide().

◆ 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 138 of file ct_utils.h.

138{ return Mask<T>::is_lt(y, x); }
Botan::CT::Mask::is_lt
static Mask< T > is_lt(T x, T y)
Definition: ct_utils.h:133

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

Referenced by Botan::CT::copy_output(), 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 148 of file ct_utils.h.

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

Referenced by Botan::ct_divide_word(), 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 133 of file ct_utils.h.

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

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 143 of file ct_utils.h.

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

Referenced by Botan::TLS::check_tls_cbc_padding().

◆ is_set()

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

Return true iff this mask is set

Definition at line 271 of file ct_utils.h.

271{ return unpoisoned_value() != 0; }
Botan::CT::Mask::unpoisoned_value
T unpoisoned_value() const
Definition: ct_utils.h:262

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 150 of file ct_utils.h.

150 {
151 //return Mask<T>::is_gte(v, l) & Mask<T>::is_lte(v, u);
152
153 const T v_lt_l = v ^ ((v ^ l) | ((v - l) ^ v));
154 const T v_gt_u = u ^ ((u ^ v) | ((u - v) ^ u));
155 const T either = v_lt_l | v_gt_u;
156 return ~Mask<T>(expand_top_bit(either));
157 }

References Botan::expand_top_bit(), and T.

◆ is_zero()

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

Return a Mask<T> which is set if v is == 0 or cleared otherwise

Definition at line 123 of file ct_utils.h.

123{ return Mask<T>(ct_is_zero<T>(x)); }

Referenced by Botan::CT::all_zeros(), Botan::bigint_cmp(), Botan::bigint_ct_is_eq(), Botan::bigint_ct_is_lt(), Botan::ct_compare_u8(), Botan::BigInt::ct_reduce_below(), Botan::CT::Mask< T >::is_equal(), Botan::oaep_find_delim(), Botan::CT::strip_leading_zeros(), Botan::OneAndZeros_Padding::unpad(), Botan::ESP_Padding::unpad(), and Botan::EME_PKCS1v15::unpad().

◆ operator&=()

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

AND-combine two masks

Definition at line 174 of file ct_utils.h.

174 {
175 m_mask &= o.value();
176 return (*this);
177 }

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 182 of file ct_utils.h.

182 {
183 m_mask ^= o.value();
184 return (*this);
185 }

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 190 of file ct_utils.h.

190 {
191 m_mask |= o.value();
192 return (*this);
193 }

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 213 of file ct_utils.h.

213{ return Mask<T>(~value()); }
Botan::CT::Mask::value
T value() const
Definition: ct_utils.h:276

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 228 of file ct_utils.h.

228{ return choose(value(), x, y); }
Botan::choose
constexpr T choose(T mask, T a, T b)
Definition: bit_ops.h:178

References Botan::choose(), 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 230 of file ct_utils.h.

230 {
231 T r = this->select(x, y);
232 CT::unpoison(r);
233 return r;
234 }
Botan::CT::Mask::select
T select(T x, T y) const
Definition: ct_utils.h:228
Botan::CT::unpoison
void unpoison(const T *p, size_t n)
Definition: ct_utils.h:57

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 239 of file ct_utils.h.

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

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 245 of file ct_utils.h.

245 {
246 for(size_t i = 0; i != len; ++i)
247 output[i] = this->select(x[i], y[i]);
248 }

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 99 of file ct_utils.h.

99{ return Mask<T>(static_cast<T>(~0)); }

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 262 of file ct_utils.h.

262 {
263 T r = value();
264 CT::unpoison(r);
265 return r;
266 }

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

Return the underlying value of the mask

Definition at line 276 of file ct_utils.h.

276{ return m_mask; }

Referenced by Botan::CT::Mask< T >::expand(), Botan::CT::Mask< T >::operator&=(), Botan::CT::Mask< T >::operator^=(), Botan::CT::Mask< T >::operator|=(), Botan::CT::Mask< T >::operator~(), Botan::CT::Mask< T >::select(), Botan::CT::Mask< T >::select_mask(), and Botan::CT::Mask< T >::unpoisoned_value().

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 198 of file ct_utils.h.

198{ return Mask<T>(x.value() & y.value()); }

◆ operator^

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

XOR-combine two masks

Definition at line 203 of file ct_utils.h.

203{ return Mask<T>(x.value() ^ y.value()); }

◆ operator|

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

OR-combine two masks

Definition at line 208 of file ct_utils.h.

208{ return Mask<T>(x.value() | y.value()); }
The documentation for this class was generated from the following file:
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