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Reimplement removing of PKCS#1 v1.5 padding to be time constant
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,128 @@ | ||
| /* Original source: https://github.com/openssl/openssl/blob/9890cc42daff5e2d0cad01ac4bf78c391f599a6e/include/internal/constant_time.h */ | ||
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| #ifndef CONSTANT_TIME_H | ||
| #define CONSTANT_TIME_H | ||
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| #include <stdlib.h> | ||
| #include <string.h> | ||
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| #if !defined(inline) | ||
| #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L | ||
| #define constant_inline inline | ||
| #elif defined(__GNUC__) && __GNUC__ >= 2 | ||
| #elif defined(__GNUC__) && __GNUC__ >= 2 | ||
| #elif defined(_MSC_VER) | ||
| #define constant_inline __inline | ||
| #else | ||
| #define constant_inline | ||
| #endif | ||
| #else /* use what caller wants as inline may be from config.h */ | ||
| #define constant_inline inline /* inline */ | ||
| #endif | ||
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| /*- | ||
| * The boolean methods return a bitmask of all ones (0xff...f) for true | ||
| * and 0 for false. For example, | ||
| * if (a < b) { | ||
| * c = a; | ||
| * } else { | ||
| * c = b; | ||
| * } | ||
| * can be written as | ||
| * unsigned int lt = constant_time_lt(a, b); | ||
| * c = constant_time_select(lt, a, b); | ||
| */ | ||
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| static constant_inline unsigned int | ||
| value_barrier(unsigned int a) | ||
| { | ||
| volatile unsigned int r = a; | ||
| return r; | ||
| } | ||
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| static constant_inline size_t | ||
| value_barrier_s(size_t a) | ||
| { | ||
| volatile size_t r = a; | ||
| return r; | ||
| } | ||
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| /* MSB */ | ||
| static constant_inline size_t | ||
| constant_time_msb_s(size_t a) | ||
| { | ||
| return 0 - (a >> (sizeof(a) * 8 - 1)); | ||
| } | ||
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| static constant_inline unsigned int | ||
| constant_time_msb(unsigned int a) | ||
| { | ||
| return 0 - (a >> (sizeof(a) * 8 - 1)); | ||
| } | ||
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| /* Select */ | ||
| static constant_inline unsigned int | ||
| constant_time_select(unsigned int mask, unsigned int a, unsigned int b) | ||
| { | ||
| return (value_barrier(mask) & a) | (value_barrier(~mask) & b); | ||
| } | ||
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| static constant_inline unsigned char | ||
| constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b) | ||
| { | ||
| return (unsigned char)constant_time_select(mask, a, b); | ||
| } | ||
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| static constant_inline size_t | ||
| constant_time_select_s(size_t mask, size_t a, size_t b) | ||
| { | ||
| return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b); | ||
| } | ||
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| /* Zero */ | ||
| static constant_inline unsigned int | ||
| constant_time_is_zero(unsigned int a) | ||
| { | ||
| return constant_time_msb(~a & (a - 1)); | ||
| } | ||
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| static constant_inline size_t | ||
| constant_time_is_zero_s(size_t a) | ||
| { | ||
| return constant_time_msb_s(~a & (a - 1)); | ||
| } | ||
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| /* Comparison*/ | ||
| static constant_inline size_t | ||
| constant_time_lt_s(size_t a, size_t b) | ||
| { | ||
| return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b))); | ||
| } | ||
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| static constant_inline unsigned int | ||
| constant_time_lt(unsigned int a, unsigned int b) | ||
| { | ||
| return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); | ||
| } | ||
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| static constant_inline unsigned int | ||
| constant_time_ge(unsigned int a, unsigned int b) | ||
| { | ||
| return ~constant_time_lt(a, b); | ||
| } | ||
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| /* Equality*/ | ||
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| static constant_inline unsigned int | ||
| constant_time_eq(unsigned int a, unsigned int b) | ||
| { | ||
| return constant_time_is_zero(a ^ b); | ||
| } | ||
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| static constant_inline size_t | ||
| constant_time_eq_s(size_t a, size_t b) | ||
| { | ||
| return constant_time_is_zero_s(a ^ b); | ||
| } | ||
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| #endif /* CONSTANT_TIME_H */ |
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