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90 lines
3.2 KiB
90 lines
3.2 KiB
##
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## Maximum password lengths vary depending on kernel, hash type, and encoding
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##
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See https://hashcat.net/faq/lengths
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##
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## Generic hash modes only support salt lengths up to 256
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##
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This limitation on salt lengths only affects generic hash modes, such as md5(pass.salt).
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Dedicated hash modes allow unlimited salt length support.
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##
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## File and folder names including UTF-16 characters are not supported
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##
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UTF-16 is mostly seen on Windows. UTF-8 (as mostly used on Linux and macOS) are fine.
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Important: That does not mean UTF-16 file content, which is fully supported.
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It only means the filename itself.
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##
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## Hashing algorithms that internally use UTF-16 characters could in special cases lead to false negatives
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##
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This applies to optimized kernels (-O) only:
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The UTF-16 conversion implementation used within the kernel code is optimized for performance. For that
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reason, hashcat does not respect all complicated encoding rules required to correctly convert, for instance,
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ASCII or UTF-8 to UTF-16LE (or UTF-16BE). The implementation most likely fails with multi-byte characters,
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because we basically add a zero byte every second byte within the kernel conversion code.
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Since hashcat v6.2.1 there is true UTF-16 support for pure kernels. UTF-16 is fully supported.
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There is an exception for mask attacks combined with compute devices that require vector data-types
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to achieve full performance. For example a modern CPU. For these devices, the recommendation is to use a
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combination of mask processor piped to hashcat. For modern GPUs it works as expected.
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##
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## The use of --keep-guessing eventually skips reporting duplicate passwords
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##
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This does not mean that valid passwords are skipped; they are always reported.
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Only if you hit the same password twice for the same hash the password may be shown only once.
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If --keep-guessing is not used, this can not occur.
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This limitation cannot be fixed, because it would require too much device (GPU/CPU) memory. If we wanted
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to report back all possible password candidates executed in a single kernel invocation, it would require
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this much memory per device:
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Number-of-MCU * Max-threads * Max-accel * Max-inner-loops * sizeof (plain_t)
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For example, on a Vega64: 64 * 1024 * 1024 * 1024 * 20 = 1,374,389,534,720 bytes = 1280 GB VRAM
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##
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## Hashcat GPU memory usage may be limited by maximum memory allocation sizes of OpenCL drivers
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##
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Most hashcat memory allocations are supposed to remain inside the same memory area.
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The maximum size of a memory allocation is limited by GPU drivers / OpenCL runtimes.
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Only a few modes (like scrypt) have special workarounds to make use of more than one allocation.
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##
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## The maximum number of functions per rule is limited to 31
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##
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This makes the size of one rule 128 byte.
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On the other hand, there is a 25% OpenCL single allocation memory limit.
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A typical GPU of today has 8GB = 2GB/128 = 16M rules max
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If hashcat supported more functions per rule, it would be limited to fewer rules.
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This is a trade-off game.
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##
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## Position identifiers in rules are limited to 36
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##
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The upper limit of maximum 36 positions for various rule functions (0-9, A-Z) was a design decision by the original authors of the rule engine.
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