Size_scrypt * number of parallel computations Step 3: Calculate RAM requirement per GPU Threads per compute unit * number of compute units = Number of parallel computations Step 2: Calculate Parallel Computations per GPU Step 1: Calculate Single Computation per GPU There are a couple of calculations required to derive the RAM required to GPU crack and remember these are GPU RAM requirements, not system ones. So the reason some of your systems hang when starting hashcat is because the N results in hashcat trying to use more RAM than your GPUs have. When deciding whether we can crack scrypt with GPUs, the most important factor is N (note that the JSON file will refer to N as n, however I’ll stick to correct notation). If you’re a glutton for detail you can find more on these parameters in scrypt’s RFC here, however at a high level they relate to work factor/iteration count, underlying hash blocksize and parallelization factor, respectively. Scrypt is an anti-GPU algorithm and depending on the scrypt parameters ( N, r and p) there’s a fair chance you’ll have to resort to CPU cracking. Since writing about cracking various Ethereum wallets using the JSON file, a few people have mentioned that their systems hang/blue screen when they start the crack, so I thought I’d talk about why this is. You’ll only be able to crack with a CPU (adding -D 1 # where # is the number hashcat assigns your CPU will select all available CPU devices, or -D 1 -d for an individual CPU) and the hash rate will still be slow □ Tl dr – If hashcat crashes/hangs your system, your wallet scrypt settings more than likely want more RAM than your GPU has. First of all, happy new year everyone! □
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