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/*
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*******************************************************************************
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\file belt_ctr.c
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\brief STB 34.101.31 (belt): CTR encryption
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\project bee2 [cryptographic library]
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\author (C) Sergey Agievich [agievich@{bsu.by|gmail.com}]
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\created 2012.12.18
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\version 2020.03.24
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\license This program is released under the GNU General Public License
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version 3. See Copyright Notices in bee2/info.h.
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*******************************************************************************
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*/
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#include "bee2/core/blob.h"
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#include "bee2/core/err.h"
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#include "bee2/core/mem.h"
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#include "bee2/core/u32.h"
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#include "bee2/core/util.h"
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#include "bee2/crypto/belt.h"
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#include "belt_lcl.h"
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/*
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*******************************************************************************
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Шифрование в режиме CTR
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Для ускорения работы счетчик ctr хранится в виде [4]u32. Это позволяет
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зашифровывать счетчик с помощью функции beltBlockEncr2(), в которой
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не используется реверс октетов даже на платформах BIG_ENDIAN.
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Реверс применяется только перед использованием зашифрованного счетчика
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в качестве гаммы.
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*******************************************************************************
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*/
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1
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size_t beltCTR_keep()
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{
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1
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return sizeof(belt_ctr_st);
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}
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1
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void beltCTRStart(void* state, const octet key[], size_t len,
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const octet iv[16])
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{
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belt_ctr_st* st = (belt_ctr_st*)state;
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1
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ASSERT(memIsDisjoint2(iv, 16, state, beltCTR_keep()));
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beltKeyExpand2(st->key, key, len);
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u32From(st->ctr, iv, 16);
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beltBlockEncr2(st->ctr, st->key);
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st->reserved = 0;
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}
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1
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void beltCTRStepE(void* buf, size_t count, void* state)
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{
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belt_ctr_st* st = (belt_ctr_st*)state;
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ASSERT(memIsDisjoint2(buf, count, state, beltCTR_keep()));
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// есть резерв гаммы?
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if (st->reserved)
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{
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1
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if (st->reserved >= count)
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{
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memXor2(buf, st->block + 16 - st->reserved, count);
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st->reserved -= count;
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1
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return;
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}
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1
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memXor2(buf, st->block + 16 - st->reserved, st->reserved);
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1
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count -= st->reserved;
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buf = (octet*)buf + st->reserved;
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st->reserved = 0;
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}
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// цикл по полным блокам
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1
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while (count >= 16)
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{
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1
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beltBlockIncU32(st->ctr);
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beltBlockCopy(st->block, st->ctr);
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beltBlockEncr2((u32*)st->block, st->key);
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#if (OCTET_ORDER == BIG_ENDIAN)
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beltBlockRevU32(st->block);
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#endif
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beltBlockXor2(buf, st->block);
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buf = (octet*)buf + 16;
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count -= 16;
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}
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// неполный блок?
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1
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if (count)
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{
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1
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beltBlockIncU32(st->ctr);
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beltBlockCopy(st->block, st->ctr);
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beltBlockEncr2((u32*)st->block, st->key);
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#if (OCTET_ORDER == BIG_ENDIAN)
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beltBlockRevU32(st->block);
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#endif
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1
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memXor2(buf, st->block, count);
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1
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st->reserved = 16 - count;
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}
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}
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err_t beltCTR(void* dest, const void* src, size_t count,
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const octet key[], size_t len, const octet iv[16])
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{
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void* state;
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// проверить входные данные
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1
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if (len != 16 && len != 24 && len != 32 ||
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!memIsValid(src, count) ||
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!memIsValid(key, len) ||
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!memIsValid(iv, 16) ||
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1
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!memIsValid(dest, count))
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0
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return ERR_BAD_INPUT;
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// создать состояние
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1
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state = blobCreate(beltCTR_keep());
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1
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if (state == 0)
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0
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return ERR_OUTOFMEMORY;
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// зашифровать
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1
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beltCTRStart(state, key, len, iv);
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1
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memMove(dest, src, count);
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1
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beltCTRStepE(dest, count, state);
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// завершить
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1
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blobClose(state);
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1
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return ERR_OK;
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}
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agievich