base36 | Base36 string encode and decode | Messaging library

I want to encode and decode Bytes from an Uint8Array (or an ArrayBuffer) to/from a string in Base36. JavaScript has the toString and parseInt functions which both support base36 but I am not sure if first converting 8 Bytes to a 64 bit floating point is the right idea.

In JS one can encode a BigInt (a number of arbitrary length) in Base36. However the other direction does not work.

How can I do this?

I've been given the challenge to find the seed from a series of pseudo-randomly generated alphanumerical IDs and after some analysis, I'm stuck in a dead end that I hope you'll be able to get me out of.

Each ID is obtained by passing the previous one through the encryption algorithm, that I'm supposed to reverse engineer in order to find the seed. The list given to me is composed of the 2070 first IDs (without the seed obviously). The IDs start as 4 alphanumerical characters, and switch to 5 after some time (e.g. "2xm1", "34nj", "avdfe", "2lgq9")

This switch happens once the algorithm, after encrypting an ID, returns an ID that has already been generated previously. At this point, it adds one character to this returned ID, making it longer and thus unique. It then proceeds as usual, generating IDs of the new length. This effectively means that the generation algorithm is surjective.

My first reflex was to try to convert those IDs from base36 to some other base, notably decimal. I used the results to scatter plot a chart of the IDs' decimal values in terms of their rank in the list, when I noticed a pattern that I couldn't understand the origin of.

After isolating the two parts of the list in terms of ID length, I scatter plotted the same graph for the 4-characters IDs sub-list and 5-characters IDs sub-list, allowing me to notice the strange density patterns.

After some analysis, I've observed 2 things :

• For each sub-list, the delimitation between the 2 densities is 6x36^(n-1), n being the number of characters in the ID. In other terms, it is 1/6th of the entire range of values for a given ID length. The range of values is [0; (36^n)-1]
• The repartition of those IDs in relation to this limit tends towards 50/50, half of them being above the 1/6th limit, half of them being under it.

I've tried to correlate such a behavior with other known PRNG scatter-plots, but none of them matched what I get on my graphs.

I'm hoping some of you might know about an encryption method, formula, or function matching such a specific scatter plot, or have any idea about what could be going on behind the scenes.

Thanks in advance for your answers.

I have some models where I use a custom non-sequential unique id, similar to a standard UUIDs. They are 64 bits long, which should last me over 8000 years, so I store them as an unsigned big integer.

However as a base10 number they are a bit long and unwieldy at 19 digits. To help with this I can transform them into a base36 number (a string containing 0-9 and a-z). They max out at 15 chars, though it should be only 11 or 12 for the next 30 years or so.

My question is whether there is a way to hook into Laravel's type hinted dependency injection so that a constructor method like this:

I want to base36 encode 128bit hexadecimal number, but 128bit exceeds the range of the largest number supported by c language. So, i can't get the value of 36 numbers by finding the remainder and finding the quotient.

I'm curious about the internal algorithm in base36 that handles such long strings. I am wondering how to express the number that cannot be expressed in the number range of c language. Can you tell me about the algorithm for base36? Or, I would like a book or site for reference.

I'm reading an online document that explains how to design a url shortening service. The website is https://www.educative.io/courses/grokking-the-system-design-interview .

In the section, Encoding actual URL, they said -> "We can compute a unique hash (e.g., MD5 or SHA256, etc.) of the given URL. The hash can then be encoded for displaying. This encoding could be base36 ([a-z ,0-9]) or base62 ([A-Z, a-z, 0-9]) and if we add ‘+’ and ‘/’ we can use Base64 encoding. A reasonable question would be, what should be the length of the short key? 6, 8, or 10 characters."

"If we use the MD5 algorithm as our hash function, it’ll produce a 128-bit hash value. After base64 encoding, we’ll get a string having more than 21 characters (since each base64 character encodes 6 bits of the hash value).Since we only have space for 8 characters per short key, how will we choose our key then? We can take the first 6 (or 8) letters for the key. This could result in key duplication, to resolve that, we can choose some other characters out of the encoding string or swap some characters."

I used online MD5 hash generator (http://onlinemd5.com/) and Base64 encoder (https://www.base64encode.org/) to verify the above. I used "www.yahoo.com" as the input string for MD5 hash and output is 1B03577ED104F16AADC00A639D33CB44 . Then I Base64 encoded it and got MUIwMzU3N0VEMTA0RjE2QUFEQzAwQTYzOUQzM0NCNDQ= with UTF-8 destination charset and Unix newline seperator.

Can anyone explain if I'm doing it correctly? I see the number of characters are way more than 21.

I have been migrating javascript code to python and I am stuck trying to get a python version of Math.random().toString(36)

I'm not sure how to do this since Math.random() returns a float, in python I have not been able to figure out how to convert a float to base36. From what I understand it's only int but then how does javascript do it?

for getting a random float in python I just use the following:

I want to add reset/forgot password functionality to my personal express.js app. I decided to implement it in similar way how Django does it.

Basically, it generates unique token based on user (id, hashed password, email, last login time and current time, all mixed with unqiue password and salt). Then, user receives that token in his "reset password link". Someone explained it better than me in one of stackoverflow answers.

And here is the source code of Django PasswordResetTokenGenerator class

I will post my javascript implementation on the bottom. It would be nice if you check it for possible flaws, but it is not my main question :)

So, user gets e-mail with "reset password link". Link looks like this https://example.com/reset-password/MQ/58ix7l-35858854f74c35d0c64a5a17bd127f71cd3ad1da, where:

• MQ is base64 encoded user id (1 in this example)
• 58ix7l is base36 encoded timestamp
• 35858... is actual token

User clicks on link. Server receives GET request -> server checks if user with that id exist -> then server checks correctness of the token. If everything is OK, server sends user html response with "set new password" form.

So far, everything was almost exactly the same how django does it (few minor differences). But now I want to do somewhat different. Django (after receiving GET request) establishes anonymous session, stores token in session, and redirect (302) to reset password form. There is no any sign of token on the client side. User fills a form, POST request is send to server with new password. Server checks token (stored in session) again. If everything is right - password is changed.

For some reason (it will make my app a lot more complicated :)), I don't want to add anonymous session, I don't want to store token in session.

I want to just take token from req.params -> escape it -> check if it is valid -> and send to user with form, like this:

I can use the strtol function for turning a base36 based value (saved as a string) into a long int: