Document and slightly reorganize mod_pXXX
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Manuel Pégourié-Gonnard
parent
2a08c0debc
commit
210b458ddc
164
library/ecp.c
164
library/ecp.c
@ -483,9 +483,20 @@ cleanup:
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}
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#if defined(POLARSSL_ECP_DP_SECP192R1_ENABLED)
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/*
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* Compared to the way things are presented in FIPS 186-3 D.2,
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* we proceed in columns, from right (least significant chunk) to left,
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* adding chunks to N in place, and keeping a carry for the next chunk.
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* This avoids moving things around in memory, and uselessly adding zeros,
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* compared to the more straightforward, line-oriented approach.
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*
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* For this prime we need to handle data in chunks of 64 bits.
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* Since this is always a multiple of our basic t_uint, we can
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* use a t_uint * to designate such a chunk, and small loops to handle it.
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*/
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/* Add 64-bit chunks (dst += src) and update carry */
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static inline void add_64( t_uint *dst, t_uint *src, t_uint *carry )
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static inline void add64( t_uint *dst, t_uint *src, t_uint *carry )
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{
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unsigned char i;
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t_uint c = 0;
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@ -508,11 +519,11 @@ static inline void carry64( t_uint *dst, t_uint *carry )
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}
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}
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#define OFFSET ( 8 / sizeof( t_uint ) )
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#define A( i ) ( N->p + ( i ) * OFFSET )
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#define ADD( i ) add_64( p, A( i ), &c )
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#define NEXT p += OFFSET; carry64( p, &c )
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#define LAST p += OFFSET; *p = c; while( ++p < end ) *p = 0
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#define WIDTH 8 / sizeof( t_uint )
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#define A( i ) N->p + i * WIDTH
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#define ADD( i ) add64( p, A( i ), &c )
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#define NEXT p += WIDTH; carry64( p, &c )
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#define LAST p += WIDTH; *p = c; while( ++p < end ) *p = 0
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/*
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* Fast quasi-reduction modulo p192 (FIPS 186-3 D.2.1)
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@ -523,8 +534,9 @@ static int ecp_mod_p192( mpi *N )
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t_uint c = 0;
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t_uint *p, *end;
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/* Make sure we have the correct number of blocks */
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MPI_CHK( mpi_grow( N, 6 * OFFSET ) );
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/* Make sure we have enough blocks so that A(5) is legal */
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MPI_CHK( mpi_grow( N, 6 * WIDTH ) );
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p = N->p;
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end = p + N->n;
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@ -536,28 +548,35 @@ cleanup:
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return( ret );
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}
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#undef OFFSET
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#undef WIDTH
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#undef A
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#undef ADD
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#undef NEXT
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#undef LAST
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#endif /* POLARSSL_ECP_DP_SECP192R1_ENABLED */
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#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED)
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#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED) || \
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defined(POLARSSL_ECP_DP_SECP256R1_ENABLED) || \
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defined(POLARSSL_ECP_DP_SECP384R1_ENABLED)
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/*
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* The reader is advised to first understand ecp_mod_p192() since the same
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* general structure is used here, but with additional complications:
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* (1) chunks of 32 bits, and (2) subtractions.
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*/
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static inline void add32( uint32_t *dst, uint32_t src, signed char *carry )
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{
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*dst += src;
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*carry += ( *dst < src );
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}
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/*
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* For these primes, we need to handle data in chunks of 32 bits.
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* This makes it more complicated if we use 64 bits limbs in MPI,
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* which prevents us from using a uniform access method as for p192.
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*
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* So, we define a mini abstraction layer to access 32 bit chunks,
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* load them in 'cur' for work, and store them back from 'cur' when done.
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*
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* While at it, also define the size of N in terms of 32-bit chunks.
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*/
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#define LOAD32 cur = A( i );
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static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
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{
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*carry -= ( *dst < src );
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*dst -= src;
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}
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#if defined(POLARSSL_HAVE_INT8)
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#if defined(POLARSSL_HAVE_INT8) /* 8 bit */
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#define MAX32 N->n / 4
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#define A( j ) (uint32_t)( N->p[4*j+0] ) | \
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@ -569,20 +588,20 @@ static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
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N->p[4*i+2] = (uint8_t)( cur >> 16 ); \
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N->p[4*i+3] = (uint8_t)( cur >> 24 );
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#elif defined(POLARSSL_HAVE_INT16)
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#elif defined(POLARSSL_HAVE_INT16) /* 16 bit */
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#define MAX32 N->n / 2
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#define A( j ) (uint32_t)( N->p[2*j] ) | ( N->p[2*j+1] << 16 )
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#define STORE32 N->p[2*i+0] = (uint16_t)( cur ); \
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N->p[2*i+1] = (uint16_t)( cur >> 16 );
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#elif defined(POLARSSL_HAVE_INT32)
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#elif defined(POLARSSL_HAVE_INT32) /* 32 bit */
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#define MAX32 N->n
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#define A( j ) N->p[j]
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#define STORE32 N->p[i] = cur;
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#else /* 64-bit */
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#else /* 64-bit */
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#define MAX32 N->n * 2
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#define A( j ) j % 2 ? (uint32_t)( N->p[j/2] >> 32 ) : (uint32_t)( N->p[j/2] )
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@ -595,14 +614,37 @@ static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
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N->p[i/2] |= (uint64_t) cur; \
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}
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#endif
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#endif /* sizeof( t_uint ) */
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/*
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* Helpers for addition and subtraction of chunks, with signed carry.
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*/
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static inline void add32( uint32_t *dst, uint32_t src, signed char *carry )
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{
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*dst += src;
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*carry += ( *dst < src );
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}
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static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
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{
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*carry -= ( *dst < src );
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*dst -= src;
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}
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#define ADD( j ) add32( &cur, A( j ), &c );
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#define SUB( j ) sub32( &cur, A( j ), &c );
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#define LOAD32 cur = A( i );
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#define FIRST c = 0; i = 0; LOAD32;
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/*
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* Helpers for the main 'loop'
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*/
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#define INIT( b ) \
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int ret; \
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signed char c = 0, cc; \
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uint32_t cur; \
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size_t i = 0, bits = b; \
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\
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MPI_CHK( mpi_grow( N, b * 2 / 8 / sizeof( t_uint ) ) ); \
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LOAD32;
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#define NEXT \
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STORE32; i++; LOAD32; \
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@ -638,22 +680,18 @@ cleanup:
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return( ret );
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}
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#endif /* POLARSSL_ECP_DP_SECP224R1_ENABLED ||
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POLARSSL_ECP_DP_SECP256R1_ENABLED ||
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POLARSSL_ECP_DP_SECP384R1_ENABLED */
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#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED)
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/*
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* Fast quasi-reduction modulo p224 (FIPS 186-3 D.2.2)
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*/
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static int ecp_mod_p224( mpi *N )
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{
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int ret;
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signed char c, cc;
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uint32_t cur;
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size_t i;
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size_t bits = 224;
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INIT( 224 );
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/* Make sure we have enough blocks */
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MPI_CHK( mpi_grow( N, bits * 2 / 8 / sizeof( t_uint ) ) );
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FIRST;
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SUB( 7 ); SUB( 11 ); NEXT; // A0 += -A7 - A11
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SUB( 8 ); SUB( 12 ); NEXT; // A1 += -A8 - A12
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SUB( 9 ); SUB( 13 ); NEXT; // A2 += -A9 - A13
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@ -667,15 +705,32 @@ cleanup:
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}
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#endif /* POLARSSL_ECP_DP_SECP224R1_ENABLED */
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#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED) || \
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defined(POLARSSL_ECP_DP_SECP256R1_ENABLED) || \
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defined(POLARSSL_ECP_DP_SECP384R1_ENABLED)
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#undef A
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#undef LOAD32
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#undef STORE32
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#undef MAX32
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#undef INIT
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#undef NEXT
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#undef LAST
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#endif /* POLARSSL_ECP_DP_SECP224R1_ENABLED ||
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POLARSSL_ECP_DP_SECP256R1_ENABLED ||
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POLARSSL_ECP_DP_SECP384R1_ENABLED */
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#if defined(POLARSSL_ECP_DP_SECP521R1_ENABLED)
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/*
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* Size of p521 in terms of t_uint
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* Here we have a real Mersenne prime, so things are more straightforward.
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* However, things are aligned on a 'weird' boundary (521 bits).
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*/
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#define P521_SIZE_INT ( 521 / 8 / sizeof( t_uint ) + 1 )
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/*
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* Bits to keep in the most significant t_uint
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*/
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/* Size of p521 in terms of t_uint */
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#define P521_WIDTH ( 521 / 8 / sizeof( t_uint ) + 1 )
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/* Bits to keep in the most significant t_uint */
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#if defined(POLARSSL_HAVE_INT8)
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#define P521_MASK 0x01
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#else
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@ -691,26 +746,26 @@ static int ecp_mod_p521( mpi *N )
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int ret;
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size_t i;
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mpi M;
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t_uint Mp[P521_SIZE_INT+1];
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/* Worst case for the size of M is when sizeof( t_uint ) == 16:
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t_uint Mp[P521_WIDTH + 1];
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/* Worst case for the size of M is when t_uint is 16 bits:
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* we need to hold bits 513 to 1056, which is 34 limbs, that is
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* P521_SIZE_INT + 1. Otherwise P521_SIZE is enough. */
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* P521_WIDTH + 1. Otherwise P521_WIDTH is enough. */
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if( N->n < P521_SIZE_INT )
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if( N->n < P521_WIDTH )
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return( 0 );
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/* M = A1 */
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M.s = 1;
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M.n = N->n - ( P521_SIZE_INT - 1 );
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if( M.n > P521_SIZE_INT + 1 )
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M.n = P521_SIZE_INT + 1;
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M.n = N->n - ( P521_WIDTH - 1 );
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if( M.n > P521_WIDTH + 1 )
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M.n = P521_WIDTH + 1;
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M.p = Mp;
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memcpy( Mp, N->p + P521_SIZE_INT - 1, M.n * sizeof( t_uint ) );
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memcpy( Mp, N->p + P521_WIDTH - 1, M.n * sizeof( t_uint ) );
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MPI_CHK( mpi_shift_r( &M, 521 % ( 8 * sizeof( t_uint ) ) ) );
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/* N = A0 */
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N->p[P521_SIZE_INT - 1] &= P521_MASK;
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for( i = P521_SIZE_INT; i < N->n; i++ )
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N->p[P521_WIDTH - 1] &= P521_MASK;
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for( i = P521_WIDTH; i < N->n; i++ )
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N->p[i] = 0;
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/* N = A0 + A1 */
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@ -719,6 +774,9 @@ static int ecp_mod_p521( mpi *N )
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cleanup:
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return( ret );
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}
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#undef P521_WIDTH
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#undef P521_MASK
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#endif /* POLARSSL_ECP_DP_SECP521R1_ENABLED */
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/*
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