Generating a random password is simple, but generating a secure one is harder if you don’t know what you’re doing. When I looked through the password generation algorithm at work, I found (and fixed) several vulnerabilities and bugs, one of which allowed a remote attacker to crack any known account with a generated password in a couple of minutes.<\/p>\n
The password generator itself was just inadequate, but an API misunderstanding made it extremely severe:<\/p>\n
The following method signature was used for the password generation:<\/p>\n
\r\npublic static string GenerateReadablePassword(int length, int seed) \r\n<\/pre>\nOn reading “int seed”, your head should be ringing with warning bells. More on that later. The real kicker was the invocation:<\/p>\n
\r\nstring Password = GenerateReadablePassword(10, DateTime.Now.Millisecond);\r\n<\/pre>\n‘<\/p>\n
If you’re familiar with the C# API, you’re likely rolling on the floor about now. Otherwise, the part about
DateTime.Now<\/code> will give you the shivers. And then you realize that this wouldn’t compile without a cast unlessDateTime.Now.Millisecond<\/code> is an int or narrower, which would make for a pretty lousy timestamp. Oh yes… This is the number of milliseconds into the current second.<\/p>\nA new account got one of 1000 possible passwords, for an effective “two characters, no uppercase or symbols” policy. <\/p>\n
Even if this had been the proper epoch time in milliseconds, it still wouldn’t have been secure. There are only 86 400 000 milliseconds in a day, and only 28 million of them are during office hours. If you can narrow it down to a specific hour, you have 3 million possible ones. And if you can hear the beep of the user’s e-mail client as the (plain-text) password e-mail is received, you’re back down to a few thousand. <\/p>\n
Going from a timestamp to an actual high quality pseudo-random seed is better, but it still doesn’t win any prizes. You then have a best case of 232<\/sup> possible passwords regardless of how long you specify the password to be. <\/p>\n
Another example of this, included in our source code, was a copy of the first google hit for “generate random password C#”. I won’t link to it in case I increase its standing. It’s a code sample that claims that it “Generates random password, which complies with the strong password rules”, and here is an excerpt:<\/p>\n
\r\n \/\/ Generate 4 random bytes.\r\n RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();\r\n rng.GetBytes(randomBytes);\r\n\r\n \/\/ Convert 4 bytes into a 32-bit integer value.\r\n int seed = (randomBytes[0] & 0x7f) << 24 |\r\n randomBytes[1] << 16 |\r\n randomBytes[2] << 8 |\r\n randomBytes[3];\r\n\r\n \/\/ Now, this is real randomization.\r\n Random random = new Random(seed);\r\n<\/pre>\nNo, this is not real randomization, this is 31 bits of high quality randomness sprinkled with a snake oil vinaigrette. Any password of any length generated by this function will not be more secure than a proper 5-character alphanumeric password. You have a secure PRNG right there! Use it!<\/p>\n","protected":false},"excerpt":{"rendered":"
Generating a random password is simple, but generating a secure one is harder if you don’t know what you’re doing. When I looked through the password generation algorithm at work, I found (and fixed) several vulnerabilities and bugs, one of which allowed a remote attacker to crack any known account with a generated password in … Continue reading “Password generation traps”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true},"categories":[22],"tags":[],"class_list":["post-11","post","type-post","status-publish","format-standard","hentry","category-security"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=11"}],"version-history":[{"count":0,"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vidarholen.net\/contents\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}