Strongbox/HmacBlockInputStream.m at master · MacPass/Strongbox · GitHub

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// HmacBlockStream.m

// Strongbox

// Created by Strongbox on 08/06/2020.

#import "HmacBlockInputStream.h"

#import "Kdbx4Serialization.h"

#import "Utils.h"

#import <CommonCrypto/CommonCrypto.h>

#import "KeePassCiphers.h"

#import "Utils.h"

@interface HmacBlockInputStream ()

@property NSUInteger workingBlockOffset;

@property uint8_t* workingBlock;

@property size_t workingBlockLength;

@property int workingBlockIndex;

@property NSData *hmacKey;

@property size_t readSoFar;

@property NSError* error;

@property NSInputStream* innerStream;

@property BOOL finished;

@end

@implementation HmacBlockInputStream

- (instancetype)initWithStream:(NSInputStream *)stream hmacKey:(NSData *)hmacKey {

if (self = [super init]) {

if (!stream) {

return nil;

}

self.workingBlock = nil;

self.workingBlockOffset = 0;

self.workingBlockIndex = 0;

self.hmacKey = hmacKey;

self.innerStream = stream;

self.finished = NO;

}

return self;

}

- (void)open {

if (self.innerStream) {

[self.innerStream open];

}

- (void)close {

if (self.innerStream) {

[self.innerStream close];

self.innerStream = nil;

}

if (self.workingBlock) {

free(self.workingBlock);

}

self.workingBlock = nil;

}

- (NSInteger)read:(uint8_t *)buffer maxLength:(NSUInteger)maxLength {

NSUInteger bufferWritten = 0;

NSUInteger bufferOffset = 0;

while (bufferWritten < maxLength) {

NSUInteger bufferAvailable = maxLength - bufferWritten;

NSUInteger workingAvailable = self.workingBlockLength - self.workingBlockOffset;

if (self.workingBlock == nil || workingAvailable == 0) {

if (! [self loadNextBlock] ) {

return -1;

}

if (self.workingBlockLength == 0) {

break;

}

workingAvailable = self.workingBlockLength - self.workingBlockOffset;

NSUInteger bytesToWriteToBuffer = MIN(bufferAvailable, workingAvailable);

uint8_t *src = &self.workingBlock[self.workingBlockOffset];

uint8_t *dest = &buffer[bufferOffset];

memcpy(dest, src, bytesToWriteToBuffer);

bufferWritten += bytesToWriteToBuffer;

bufferOffset += bytesToWriteToBuffer;

self.workingBlockOffset += bytesToWriteToBuffer;

}

return bufferWritten;

}

- (BOOL)loadNextBlock {

if (self.finished) {

if (self.workingBlock) {

free(self.workingBlock);

}

self.workingBlock = nil;

self.workingBlockLength = 0;

return YES;

}

HmacBlockHeader blockHeader;

NSInteger bytesRead = [self.innerStream read:(uint8_t*)&blockHeader maxLength:SIZE_OF_HMAC_BLOCK_HEADER];

if (bytesRead != SIZE_OF_HMAC_BLOCK_HEADER) {

return NO;

}

size_t blockLength = littleEndian4BytesToUInt32(blockHeader.lengthBytes);

if (blockLength > 0) {

if (self.workingBlock != nil) {

free(self.workingBlock);

}

self.workingBlock = malloc(blockLength);

bytesRead = [self.innerStream read:self.workingBlock maxLength:blockLength];

if(bytesRead < 0 || bytesRead < blockLength) {

NSLog(@"Not enough data to decrypt Block! [%@]", self.innerStream.streamError);

self.error = self.innerStream.streamError ? self.innerStream.streamError : [Utils createNSError:@"Error: HmacBlocStream - Could not read enough from inner stream to decrypt block." errorCode:-1];

free(self.workingBlock);

self.workingBlock = nil;

self.workingBlockLength = 0;

self.finished = YES;

return NO;

}

self.workingBlockLength = blockLength;

NSData *actualHmac = getBlockHmacBytes(self.workingBlock, self.workingBlockLength, self.hmacKey, self.workingBlockIndex);

NSData *expectedHmac = [NSData dataWithBytes:blockHeader.hmacSha256 length:CC_SHA256_DIGEST_LENGTH];

if(![actualHmac isEqualToData:expectedHmac]) {

NSLog(@"Actual Block HMAC does not match expected. Block has been corrupted.");

self.error = [Utils createNSError:@"Actual Block HMAC does not match expected. Block has been corrupted." errorCode:-1];

self.workingBlock = nil;

self.finished = YES;

return NO;

}

else {

if (self.workingBlock) {

free(self.workingBlock);

}

self.workingBlock = nil;

self.workingBlockLength = 0;

self.finished = YES;

}

self.readSoFar += blockLength;

self.workingBlockIndex++;

self.workingBlockOffset = 0;

return YES;

}

NSData* getBlockHmac(NSData *data, NSData* hmacKey, uint64_t blockIndex) {

return getBlockHmacBytes((uint8_t*)data.bytes, data.length, hmacKey, blockIndex);

}

NSData* getBlockHmacBytes(const uint8_t* data, size_t len, NSData* hmacKey, uint64_t blockIndex) {

NSData* blockKey = getHmacKeyForBlock(hmacKey, blockIndex);

NSData* index = Uint64ToLittleEndianData(blockIndex);

NSData* blockSizeData = Uint32ToLittleEndianData((uint32_t)len);

CCHmacContext ctx;

CCHmacInit(&ctx, kCCHmacAlgSHA256, blockKey.bytes, blockKey.length);

CCHmacUpdate(&ctx, index.bytes, index.length);

CCHmacUpdate(&ctx, blockSizeData.bytes, blockSizeData.length);

if(len){

CCHmacUpdate(&ctx, data, len);

}

NSMutableData *hmac = [NSMutableData dataWithLength:CC_SHA256_DIGEST_LENGTH];

CCHmacFinal(&ctx, hmac.mutableBytes);

return hmac;

}

NSData* getHmacKeyForBlock(NSData* key, uint64_t blockIndex) {

NSData* index = Uint64ToLittleEndianData(blockIndex);

NSMutableData *hash = [NSMutableData dataWithLength:CC_SHA512_DIGEST_LENGTH];

CC_SHA512_CTX ctx;

CC_SHA512_Init(&ctx);

CC_SHA512_Update(&ctx, index.bytes, (CC_LONG)index.length);

CC_SHA512_Update(&ctx, key.bytes, (CC_LONG)key.length);

CC_SHA512_Final(hash.mutableBytes, &ctx);

return hash;

}

- (NSError *)streamError {

return self.error;

}

@end

Strongbox/HmacBlockInputStream.m at master · MacPass/Strongbox · GitHub

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