If in doubt, create a longer password, or pass your generated password as input to another generator, or use multi-factor authentication. And it's certainly better than using 'Pa$$w0rD' for everything. You probably know when this is useful or not. Have bad vision, but in general use of this option is not recom‐ Number of possible passwords significantly, and as such reduces Proceedings of the 2015 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies. Printed, such as 'l' and '1', or '0' or 'O'. Stil, pwgen put gives this caveat in its man page, describing its -B option: -B, -ambiguousĭon't use characters that could be confused by the user when You would want to use an option like this if you are resetting someone's password or giving a one-time passkey that needs to be communicated. However, you will at some point probably appreciate applications (like pwgen, KeePassX or LastPass) that give you an option to avoid easily confusable characters, like 1 and l and I. the sed expression strips out strips out spaces and tabs (represented by \s). To get a larger selection, pass more bytes to head, and to get longer password result strings, modify -bytes in strings (which gives a minimum length). I suspect your use case if different, but this kind of thing is useful for shared secret keys, and other kinds of passwords that you don't type in very often. But for most practical purposes, if you just be sure to generate things that are a few characters longer than you otherwise might, then your gain in strength from generating a longer password will surely overwhelm the loss of strength from their non-uniform behavior.The results are more hideous even than apg or pwgen (even with the -s option set), but this is more fun: head -c 8192 /dev/urandom | strings -bytes 8 | sed 's/\s//' It is frustrating that popular password generators are hard to actually analyze in terms of strength. So between the relatively small modulo bias and the much larger deliberate bias toward more likely sounding syllables, it would require a level of analysis beyond what I am willing to do to actually calculate the min-entropy. It is a relatively small bias that comes up through a common design error when trying to pick a number between 1 and N even when the underlying random number generator is good. I have argued that we should be using min-entropy in such cases.Īdditionally, some versions of pwgen are subject to the modulo bias. RELEASE NOTES: - Version 2.9. The pwgen application may not have this functionality built in, but as you've already noted, we can use the -r switch to accomplish the inverse. There is no clear answer to what notion of entropy is most appropriate when password creation schemes when the schemes do not produce uniform output. A link to the video of the talk and the slides are here: Note I discuss this in my PasswordConLV15 talk. This is true of most "pronounceable" password generators. This is because it tries to mimic some of the frequencies we have in English. Some passwords are more likely than others. Pwgen does not produce passwords uniformly. The actual answer to your question is too hard for me to reasonably calculate, but I can say a few useful things about this. But it is far more than enough against automatized login scripts particularly if something (like a fail2ban) causes a hard, low limit to the possible tries. It means, that pwgen is probably quite sophistically tuned also for the high entropy, and not only to produce easily pronouncable passwords.ģ6 bit is not enough defense against gpu-accelerated, clustered brute force attacks. Typically, text data can be compressed to around 10% of its original size, while xz could reach only a 60% ratio. Note: although the output was a text file, xz could compress it only with a surprisingly bad ratio. Replayed measurements didn't show a significant dispersion.īased on this, the entropy of a single, 8 byte-long pwgen password is 8*8*593412/1048576 = 36.2 bits of entropy. Generated passwords can be sent via email. Generates an 1MB long password, compresses it with the best known flags of the best known compressor, and measures the size of the output. Random password generator can generate up to 200 unique passwords at once. The command pwgen 1048576|xz -9ve -|wc -c But I think we can use a strong compressor to approximate the entropy. An exact answer would require a deeper analyzis of the pwgen source code, or a more exact measurement.
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