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* Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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FILE_LICENCE ( GPL2_OR_LATER );
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* This mechanism is designed to comply with ANS X9.82 Part 3-2007
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* Section 9. This standard is not freely available, but most of the
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* text appears to be shared with NIST SP 800-90, which can be
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* http://csrc.nist.gov/publications/nistpubs/800-90/SP800-90revised_March2007.pdf
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* Where possible, references are given to both documents. In the
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* case of any disagreement, ANS X9.82 takes priority over NIST SP
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* 800-90. (In particular, note that some algorithms that are
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* Approved by NIST SP 800-90 are not Approved by ANS X9.82.)
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#include <ipxe/entropy.h>
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#include <ipxe/drbg.h>
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* @v state Algorithm state to be initialised
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* @v personal Personalisation string
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* @v personal_len Length of personalisation string
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* @ret rc Return status code
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* This is the Instantiate_function defined in ANS X9.82 Part 3-2007
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* Section 9.2 (NIST SP 800-90 Section 9.1).
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* Only a single security strength is supported, and prediction
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* resistance is always enabled. The nonce is accounted for by
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* increasing the entropy input, as per ANS X9.82 Part 3-2007 Section
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* 8.4.2 (NIST SP 800-90 Section 8.6.7).
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int drbg_instantiate ( struct drbg_state *state, const void *personal,
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size_t personal_len ) {
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unsigned int entropy_bits = ( ( 3 * DRBG_SECURITY_STRENGTH + 1 ) / 2 );
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size_t min_len = DRBG_MIN_ENTROPY_LEN_BYTES;
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size_t max_len = DRBG_MAX_ENTROPY_LEN_BYTES;
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uint8_t data[max_len];
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DBGC ( state, "DRBG %p instantiate\n", state );
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assert ( state != NULL );
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/* 1. If requested_instantiation_security_strength >
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* highest_supported_security_strength, then return an
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if ( DRBG_SECURITY_STRENGTH > DRBG_MAX_SECURITY_STRENGTH ) {
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DBGC ( state, "DRBG %p cannot support security strength %d\n",
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state, DRBG_SECURITY_STRENGTH );
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/* 2. If prediction_resistance_flag is set, and prediction
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* resistance is not supported, then return an ERROR_FLAG
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* (Nothing to do since prediction resistance is always
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/* 3. If the length of the personalization_string >
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* max_personalization_string_length, return an ERROR_FLAG
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if ( personal_len > DRBG_MAX_PERSONAL_LEN_BYTES ) {
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DBGC ( state, "DRBG %p personalisation string too long (%zd "
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"bytes)\n", state, personal_len );
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/* 4. Set security_strength to the nearest security strength
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* greater than or equal to
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* requested_instantiation_security_strength.
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* (Nothing to do since we support only a single security
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/* 5. Using the security_strength, select appropriate DRBG
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* mechanism parameters.
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* (Nothing to do since we support only a single security
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/* 6. ( status, entropy_input ) = Get_entropy_input (
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* security_strength, min_length, max_length,
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* prediction_resistance_request )
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* 7. If an ERROR is returned in step 6, return a
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* CATASTROPHIC_ERROR_FLAG.
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len = get_entropy_input ( entropy_bits, data, min_len,
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DBGC ( state, "DRBG %p could not get entropy input: %s\n",
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state, strerror ( rc ) );
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assert ( len >= ( int ) min_len );
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assert ( len <= ( int ) sizeof ( data ) );
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/* 9. initial_working_state = Instantiate_algorithm (
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* entropy_input, nonce, personalization_string ).
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drbg_instantiate_algorithm ( state, data, len, personal, personal_len );
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/* 10. Get a state_handle for a currently empty state. If an
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* empty internal state cannot be found, return an
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* 11. Set the internal state indicated by state_handle to
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* the initial values for the internal state (i.e. set
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* the working_state to the values returned as
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* initial_working_state in step 9 and any other values
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* required for the working_state, and set the
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* administrative information to the appropriate values.
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* (Almost nothing to do since the memory to hold the state
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* was passed in by the caller and has already been updated
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state->reseed_required = 0;
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/* 12. Return SUCCESS and state_handle. */
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* @v state Algorithm state
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* @v additional Additional input
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* @v additional_len Length of additional input
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* @ret rc Return status code
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* This is the Reseed_function defined in ANS X9.82 Part 3-2007
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* Section 9.3 (NIST SP 800-90 Section 9.2).
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* Prediction resistance is always enabled.
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int drbg_reseed ( struct drbg_state *state, const void *additional,
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size_t additional_len ) {
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unsigned int entropy_bits = DRBG_SECURITY_STRENGTH;
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size_t min_len = DRBG_MIN_ENTROPY_LEN_BYTES;
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size_t max_len = DRBG_MAX_ENTROPY_LEN_BYTES;
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uint8_t data[max_len];
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DBGC ( state, "DRBG %p reseed\n", state );
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assert ( state != NULL );
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/* 1. Using state_handle, obtain the current internal state.
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* If state_handle indicates an invalid or empty internal
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* state, return an ERROR_FLAG.
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* (Almost nothing to do since the memory holding the internal
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* state was passed in by the caller.)
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if ( ! state->valid ) {
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DBGC ( state, "DRBG %p not valid\n", state );
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/* 2. If prediction_resistance_request is set, and
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* prediction_resistance_flag is not set, then return an
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* (Nothing to do since prediction resistance is always
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/* 3. If the length of the additional_input >
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* max_additional_input_length, return an ERROR_FLAG.
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if ( additional_len > DRBG_MAX_ADDITIONAL_LEN_BYTES ) {
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DBGC ( state, "DRBG %p additional input too long (%zd bytes)\n",
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state, additional_len );
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/* 4. ( status, entropy_input ) = Get_entropy_input (
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* security_strength, min_length, max_length,
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* prediction_resistance_request ).
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* 5. If an ERROR is returned in step 4, return a
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* CATASTROPHIC_ERROR_FLAG.
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len = get_entropy_input ( entropy_bits, data, min_len,
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DBGC ( state, "DRBG %p could not get entropy input: %s\n",
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state, strerror ( rc ) );
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/* 6. new_working_state = Reseed_algorithm ( working_state,
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* entropy_input, additional_input ).
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drbg_reseed_algorithm ( state, data, len, additional, additional_len );
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/* 7. Replace the working_state in the internal state
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* indicated by state_handle with the values of
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* new_working_state obtained in step 6.
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* (Nothing to do since the state has already been updated in-situ.)
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/* 8. Return SUCCESS. */
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* Generate pseudorandom bits using DRBG
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* @v state Algorithm state
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* @v additional Additional input
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* @v additional_len Length of additional input
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* @v prediction_resist Prediction resistance is required
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* @v data Output buffer
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* @v len Length of output buffer
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* @ret rc Return status code
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* This is the Generate_function defined in ANS X9.82 Part 3-2007
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* Section 9.4 (NIST SP 800-90 Section 9.3).
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* Requests must be for an integral number of bytes. Only a single
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* security strength is supported. Prediction resistance is supported
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int drbg_generate ( struct drbg_state *state, const void *additional,
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size_t additional_len, int prediction_resist,
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void *data, size_t len ) {
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DBGC ( state, "DRBG %p generate\n", state );
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assert ( state != NULL );
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assert ( data != NULL );
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/* 1. Using state_handle, obtain the current internal state
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* for the instantiation. If state_handle indicates an
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* invalid or empty internal state, then return an ERROR_FLAG.
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* (Almost nothing to do since the memory holding the internal
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* state was passed in by the caller.)
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if ( ! state->valid ) {
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DBGC ( state, "DRBG %p not valid\n", state );
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/* 2. If requested_number_of_bits >
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* max_number_of_bits_per_request, then return an
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if ( len > DRBG_MAX_GENERATED_LEN_BYTES ) {
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DBGC ( state, "DRBG %p request too long (%zd bytes)\n",
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/* 3. If requested_security_strength > the security_strength
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* indicated in the internal state, then return an
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* (Nothing to do since only a single security strength is
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/* 4. If the length of the additional_input >
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* max_additional_input_length, then return an ERROR_FLAG.
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if ( additional_len > DRBG_MAX_ADDITIONAL_LEN_BYTES ) {
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DBGC ( state, "DRBG %p additional input too long (%zd bytes)\n",
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state, additional_len );
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/* 5. If prediction_resistance_request is set, and
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* prediction_resistance_flag is not set, then return an
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* (Nothing to do since prediction resistance is always
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/* 6. Clear the reseed_required_flag. */
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state->reseed_required = 0;
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/* 7. If reseed_required_flag is set, or if
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* prediction_resistance_request is set, then
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if ( state->reseed_required || prediction_resist ) {
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/* 7.1 status = Reseed_function ( state_handle,
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* prediction_resistance_request,
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* 7.2 If status indicates an ERROR, then return
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if ( ( rc = drbg_reseed ( state, additional,
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additional_len ) ) != 0 ) {
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DBGC ( state, "DRBG %p could not reseed: %s\n",
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state, strerror ( rc ) );
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/* 7.3 Using state_handle, obtain the new internal
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* (Nothing to do since the internal state has been
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/* 7.4 additional_input = the Null string. */
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/* 7.5 Clear the reseed_required_flag. */
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state->reseed_required = 0;
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/* 8. ( status, pseudorandom_bits, new_working_state ) =
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* Generate_algorithm ( working_state,
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* requested_number_of_bits, additional_input ).
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rc = drbg_generate_algorithm ( state, additional, additional_len,
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/* 9. If status indicates that a reseed is required before
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* the requested bits can be generated, then
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/* 9.1 Set the reseed_required_flag. */
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state->reseed_required = 1;
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/* 9.2 If the prediction_resistance_flag is set, then
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* set the prediction_resistance_request
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prediction_resist = 1;
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/* 9.3 Go to step 7. */
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/* 10. Replace the old working_state in the internal state
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* indicated by state_handle with the values of
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* (Nothing to do since the working state has already been
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/* 11. Return SUCCESS and pseudorandom_bits. */
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* @v state Algorithm state
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* This is the Uninstantiate_function defined in ANS X9.82 Part 3-2007
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* Section 9.5 (NIST SP 800-90 Section 9.4).
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void drbg_uninstantiate ( struct drbg_state *state ) {
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DBGC ( state, "DRBG %p uninstantiate\n", state );
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assert ( state != NULL );
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/* 1. If state_handle indicates an invalid state, then return
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* (Nothing to do since the memory holding the internal state
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* was passed in by the caller.)
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/* 2. Erase the contents of the internal state indicated by
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memset ( state, 0, sizeof ( *state ) );
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/* 3. Return SUCCESS. */
added
removed
src/crypto/drbg.c
