Comment by stevefan1999

Comment by stevefan1999 2 days ago

9 replies

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> In my 6502 hacking days, the presence of an exclusive OR was a sure-fire indicator you’d either found the encryption part of the code, or some kind of sprite routine.

Correct. Most ciphers of that era should be Feistel cipher in the likes of DES/3DES, or even RC4 uses XOR too. Later AES/Rijndael, CRC and ECC (Elliptic Curve Cryptography) also make heavy use of XOR but in finite field terms which is based on modular arithmetic over GF(2), that effectively reduces to XOR (while in theory should be mod 2).

OhMeadhbh 2 days ago

I was going to say "but RC4 and AES were published well after the 6502's heyday," but NESes were completely rocking it in '87 (and I'm told 65XX cores were used as the basis for several hard drive controllers of the era.) Alas, the closest I ever came to encryption on a (less than 32-bit system) was lucifer on an IBM channel controller in the forever-ago and debugging RC5 on an 8085.

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  • kjs3 2 days ago

    I'm told 65XX cores were used as the basis for several hard drive controllers of the era

    Western Design Center is still (apparently) making a profit at least in part licensing 6502 core IP for embedded stuff. There's probably a 6502 buried and unrecognized in all sorts of low-cost control applications laying around you.

    RC5 on an 8085

    Oof. Well played.

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    • PaulHoule 2 days ago

      I dunno. The 6502 has been a $2 part for a long time but needs RAM and some glue logic, for a similar price you can get an AVR-8 [1] or ESP-32 [2] and get some RAM and GPIO.

      [1] faster, more registers than the IBM 360, << 64k RAM

      [2] much faster, 32bit, >> 64k RAM

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      • brucehoult 2 days ago

        65C02s are $8 now. That didn't stop me buying one when I was stuck at home during COVID. And a 6809 too.

        But forget AVR. Yeah, for a buck or so the ATTiny85 was my go-to small MCU five years ago, and the $5 328 for bigger tasks.

        But for the last three years both can be replaced by a 48 MHz 32 bit RISC-V CH32V003 for $0.10 for the 8 pin package (like ATTiny85, and also no external components needed) and $0.20 for the 20 pin package with basically the same number of GPIOs as the 328. At 2k RAM and 16K flash it's the same RAM and a little less flash than the ATMega328 -- but not as much as you'd think as RISC-V handles 16 and 32 bit values and pointers sooo much better.

        And now you have the CH32V002/4/5/6 with enhanced CPU and more RAM and/or flash -- up to 8K rAM and 62K flash on the 006 -- and still for around the $0.10-$0.20 price

        https://www.lcsc.com/product-detail/C42431288.html

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ASalazarMX 2 days ago

Reading cryptography was that advanced at that time, I'm even more surprised that the venerable Norton Utilities for MS-DOS required a password, that was simply XORed with some constant and embedded in the executables. If the reserved space was zeroes, it considered it a fresh install and demanded a new password.

If it had been properly encrypted my young cracker self would have had no opportunity.

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stevefan1999 13 hours ago

Self-correction: It is GF(2^8) and not GF(2), but GF(2^8) primitive operations (such as carryless multiplication) can be reduced into a bunch of table lookups and/or GF(2) operations, which is how to AES crypto accelerators are being done in hardware.

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Sesse__ a day ago

Well, running in CTR mode is really common now, and that ends up XORing the generated keystream into the plaintext… (CTR mode is essentially converting block ciphers into stream ciphers, if you want to see it that way.)

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