#ifndef _IPXE_ENTROPY_H
#define _IPXE_ENTROPY_H
/** @file
*
* Entropy source
*
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <stdint.h>
#include <string.h>
#include <assert.h>
#include <ipxe/api.h>
#include <ipxe/hash_df.h>
#include <ipxe/sha256.h>
#include <config/entropy.h>
/**
* Calculate static inline entropy API function name
*
* @v _prefix Subsystem prefix
* @v _api_func API function
* @ret _subsys_func Subsystem API function
*/
#define ENTROPY_INLINE( _subsys, _api_func ) \
SINGLE_API_INLINE ( ENTROPY_PREFIX_ ## _subsys, _api_func )
/**
* Provide a entropy API implementation
*
* @v _prefix Subsystem prefix
* @v _api_func API function
* @v _func Implementing function
*/
#define PROVIDE_ENTROPY( _subsys, _api_func, _func ) \
PROVIDE_SINGLE_API ( ENTROPY_PREFIX_ ## _subsys, _api_func, _func )
/**
* Provide a static inline entropy API implementation
*
* @v _prefix Subsystem prefix
* @v _api_func API function
*/
#define PROVIDE_ENTROPY_INLINE( _subsys, _api_func ) \
PROVIDE_SINGLE_API_INLINE ( ENTROPY_PREFIX_ ## _subsys, _api_func )
/** A noise sample */
typedef uint8_t noise_sample_t;
/** An entropy sample */
typedef uint8_t entropy_sample_t;
/** An amount of min-entropy
*
* Expressed as a fixed-point quantity in order to avoid floating
* point calculations.
*/
typedef unsigned int min_entropy_t;
/** Fixed-point scale for min-entropy amounts */
#define MIN_ENTROPY_SCALE ( 1 << 16 )
/**
* Construct a min-entropy fixed-point value
*
* @v bits min-entropy in bits
* @ret min_entropy min-entropy as a fixed-point value
*/
#define MIN_ENTROPY( bits ) \
( ( min_entropy_t ) ( (bits) * MIN_ENTROPY_SCALE ) )
/* Include all architecture-independent entropy API headers */
#include <ipxe/null_entropy.h>
#include <ipxe/efi/efi_entropy.h>
#include <ipxe/linux/linux_entropy.h>
/* Include all architecture-dependent entropy API headers */
#include <bits/entropy.h>
/**
* Enable entropy gathering
*
* @ret rc Return status code
*/
int entropy_enable ( void );
/**
* Disable entropy gathering
*
*/
void entropy_disable ( void );
/**
* min-entropy per sample
*
* @ret min_entropy min-entropy of each sample
*
* min-entropy is defined in ANS X9.82 Part 1-2006 Section 8.3 and in
* NIST SP 800-90 Appendix C.3 as
*
* H_min = -log2 ( p_max )
*
* where p_max is the probability of the most likely sample value.
*
* This must be a compile-time constant.
*/
min_entropy_t min_entropy_per_sample ( void );
/**
* Get noise sample
*
* @ret noise Noise sample
* @ret rc Return status code
*
* This is the GetNoise function defined in ANS X9.82 Part 2
* (October 2011 Draft) Section 6.5.2.
*/
int get_noise ( noise_sample_t *noise );
extern int get_entropy_input_tmp ( unsigned int num_samples,
uint8_t *tmp, size_t tmp_len );
/** Use SHA-256 as the underlying hash algorithm for Hash_df
*
* Hash_df using SHA-256 is an Approved algorithm in ANS X9.82.
*/
#define entropy_hash_df_algorithm sha256_algorithm
/** Underlying hash algorithm output length (in bytes) */
#define ENTROPY_HASH_DF_OUTLEN_BYTES SHA256_DIGEST_SIZE
/**
* Obtain entropy input
*
* @v min_entropy_bits Minimum amount of entropy, in bits
* @v data Data buffer
* @v min_len Minimum length of entropy input, in bytes
* @v max_len Maximum length of entropy input, in bytes
* @ret len Length of entropy input, in bytes, or negative error
*
* This is the implementation of the Get_entropy_input function (using
* an entropy source as the source of entropy input and condensing
* each entropy source output after each GetEntropy call) as defined
* in ANS X9.82 Part 4 (April 2011 Draft) Section 13.3.4.2.
*
* To minimise code size, the number of samples required is calculated
* at compilation time.
*/
static inline __attribute__ (( always_inline )) int
get_entropy_input ( unsigned int min_entropy_bits, void *data, size_t min_len,
size_t max_len ) {
size_t tmp_len = ( ( ( min_entropy_bits * 2 ) + 7 ) / 8 );
uint8_t tmp_buf[ tmp_len ];
uint8_t *tmp = ( ( tmp_len > max_len ) ? tmp_buf : data );
double min_samples;
unsigned int num_samples;
unsigned int n;
int rc;
/* Sanity checks */
linker_assert ( ( min_entropy_per_sample() <=
MIN_ENTROPY ( 8 * sizeof ( noise_sample_t ) ) ),
min_entropy_per_sample_is_impossibly_high );
linker_assert ( ( min_entropy_bits <= ( 8 * max_len ) ),
entropy_buffer_too_small );
/* Round up minimum entropy to an integral number of bytes */
min_entropy_bits = ( ( min_entropy_bits + 7 ) & ~7 );
/* Calculate number of samples required to contain sufficient entropy */
min_samples = ( MIN_ENTROPY ( min_entropy_bits ) /
min_entropy_per_sample() );
/* Round up to a whole number of samples. We don't have the
* ceil() function available, so do the rounding by hand.
*/
num_samples = min_samples;
if ( num_samples < min_samples )
num_samples++;
linker_assert ( ( num_samples >= min_samples ), rounding_error );
/* Floating-point operations are not allowed in iPXE since we
* never set up a suitable environment. Abort the build
* unless the calculated number of samples is a compile-time
* constant.
*/
linker_assert ( __builtin_constant_p ( num_samples ),
num_samples_not_constant );
/* (Unnumbered). The output length of the hash function shall
* meet or exceed the security strength indicated by the
* min_entropy parameter.
*/
linker_assert ( ( ( 8 * ENTROPY_HASH_DF_OUTLEN_BYTES ) >=
min_entropy_bits ), hash_df_algorithm_too_weak );
/* 1. If ( min_length > max_length ), then return ( FAILURE, Null ) */
linker_assert ( ( min_len <= max_len ), min_len_greater_than_max_len );
/* 2. n = 2 * min_entropy */
n = ( 2 * min_entropy_bits );
/* 3. entropy_total = 0
* 4. tmp = a fixed n-bit value, such as 0^n
* 5. While ( entropy_total < min_entropy )
* 5.1. ( status, entropy_bitstring, assessed_entropy )
* = GetEntropy()
* 5.2. If status indicates an error, return ( status, Null )
* 5.3. nonce = MakeNextNonce()
* 5.4. tmp = tmp XOR df ( ( nonce || entropy_bitstring ), n )
* 5.5. entropy_total = entropy_total + assessed_entropy
*
* (The implementation of these steps is inside the function
* get_entropy_input_tmp().)
*/
linker_assert ( __builtin_constant_p ( tmp_len ),
tmp_len_not_constant );
linker_assert ( ( n == ( 8 * tmp_len ) ), tmp_len_mismatch );
if ( ( rc = get_entropy_input_tmp ( num_samples, tmp, tmp_len ) ) != 0 )
return rc;
/* 6. If ( n < min_length ), then tmp = tmp || 0^(min_length-n)
* 7. If ( n > max_length ), then tmp = df ( tmp, max_length )
* 8. Return ( SUCCESS, tmp )
*/
if ( tmp_len < min_len ) {
/* (Data is already in-place.) */
linker_assert ( ( data == tmp ), data_not_inplace );
memset ( ( data + tmp_len ), 0, ( min_len - tmp_len ) );
return min_len;
} else if ( tmp_len > max_len ) {
linker_assert ( ( tmp == tmp_buf ), data_inplace );
hash_df ( &entropy_hash_df_algorithm, tmp, tmp_len,
data, max_len );
return max_len;
} else {
/* (Data is already in-place.) */
linker_assert ( ( data == tmp ), data_not_inplace );
return tmp_len;
}
}
#endif /* _IPXE_ENTROPY_H */
