Comments (7)
XTS is very heavy - it needs two AES128 objects internally. That will use up to 400 bytes of RAM, which is nearly a quarter of all RAM on a Uno.
The random number generator RNG also consumes about 150 bytes even if you don't use it. So if you don't need that you could remove it from the library or comment it out.
I assume that you are using XTS to encrypt sectors on the SD card? It may be possible to rearrange the code to use only 1 BlockCipher object but keeping the key passed to XTSCommon::setKey() around and then setting each half of the key on the cipher during setTweak(), encryptSector(), and decryptSector(). But it would be slower to set up keys at the start of each sector encrypt/decrypt operation.
You may have to switch to an Arduino with more memory, sorry.
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Another thing you could try is to use the AESSmall128 version of AES instead of AES128. It is slower, but it uses a lot less RAM for the key schedule.
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Ok, I'll try to start by removing the RNG function, I think 150 bytes will be enough. But is the random() Arduino built-in function not secure?
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If you need a source of random numbers for your application, then random() is not secure enough and you'll need RNG. But if you are encrypting/decrypting the SD card contents with a fixed XTS key then you may not need RNG.
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Why isn't is secure? Because of the lack of randomness? Isn't the randomSeed() function good enough to compensate?
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System random number generators like random() in Arduino and rand() in C are never safe to use for cryptographic purposes.
The randomSeed() function takes an unsigned long, which is only 32 bits of entropy, even assuming that you have a good source to get entropy from. And the random() function uses a predictable algorithm for converting one seed value into the next.
Such random number generators are fine for controlling the random firing from a monster in a video game. But not for cryptography.
Here is some more information on system random number generators: https://crypto.stackexchange.com/questions/15662/how-vulnerable-is-the-c-rand-in-public-cryptography-protocols
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Related Issues (20)
- Encrypt String longer than blockSize() HOT 5
- Asymmetric encryption/decryption? HOT 3
- Error compiling for new Arduino core for the ESP32 HOT 4
- Support for XChaCha20 Poly1305 HOT 2
- Need help with ChaCha and Strings HOT 1
- TestSpeck.ino fails on samd21 M0 after changing the plaintext HOT 1
- Asymmetric encryption HOT 1
- Including libraries does not work in platformio HOT 1
- default key? HOT 4
- Bug of Ascon128.c++ in Arduino Cryptography Library HOT 3
- TestSpeck.ino - Decryption fails for SpeckTiny with all key sizes HOT 1
- Crypto doesn't support next generation AVRs HOT 18
- ’SHA256‘ was not declared in this scope ESP32S3 HOT 6
- Crypto library "Hash.h" conflicting with ESP866 Arduino package "Hash.h" HOT 5
- Ascon128::decrypt doesn't seem to allow for inplace decryption, despite documentation saying so
- Support for SHA-512/256?
- crypto_feed_watchdog was not declared in this scope [ESP8266 & ESP32] HOT 3
- RNG.cpp include of <Arduino.h> makes native builds for unit testing and debugging fail
- Error Compiling for ESP8266 or ESP32 clean() not declared in scope AES CFB example
- calculated shared secret doesn't match (Diffie-Hellman, Curve25519)
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