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61 lines
1.9 KiB
Objective-C
61 lines
1.9 KiB
Objective-C
//
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// Copyright (c) 2018 Open Whisper Systems. All rights reserved.
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//
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#import <Foundation/Foundation.h>
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#import "OWSAsserts.h"
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#import "NSData+messagePadding.h"
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@implementation NSData (messagePadding)
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- (NSData *)removePadding {
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unsigned long paddingStart = self.length;
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Byte data[self.length];
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[self getBytes:data length:self.length];
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for (long i = (long)self.length - 1; i >= 0; i--) {
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if (data[i] == (Byte)0x80) {
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paddingStart = (unsigned long)i;
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break;
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} else if (data[i] != (Byte)0x00) {
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OWSLogWarn(@"Failed to remove padding, returning unstripped padding");
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return self;
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}
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}
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return [self subdataWithRange:NSMakeRange(0, paddingStart)];
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}
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- (NSData *)paddedMessageBody {
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// From
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// https://github.com/signalapp/TextSecure/blob/master/libtextsecure/src/main/java/org/whispersystems/textsecure/internal/push/PushTransportDetails.java#L55
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// NOTE: This is dumb. We have our own padding scheme, but so does the cipher.
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// The +1 -1 here is to make sure the Cipher has room to add one padding byte,
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// otherwise it'll add a full 16 extra bytes.
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NSUInteger paddedMessageLength = [self paddedMessageLength:(self.length + 1)] - 1;
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NSMutableData *paddedMessage = [NSMutableData dataWithLength:paddedMessageLength];
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Byte paddingByte = 0x80;
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[paddedMessage replaceBytesInRange:NSMakeRange(0, self.length) withBytes:[self bytes]];
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[paddedMessage replaceBytesInRange:NSMakeRange(self.length, 1) withBytes:&paddingByte];
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return paddedMessage;
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}
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- (NSUInteger)paddedMessageLength:(NSUInteger)messageLength {
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NSUInteger messageLengthWithTerminator = messageLength + 1;
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NSUInteger messagePartCount = messageLengthWithTerminator / 160;
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if (messageLengthWithTerminator % 160 != 0) {
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messagePartCount++;
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}
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return messagePartCount * 160;
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}
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@end
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