Re: Encrypting a short string?
Hi Erik, I really don't recommend the ROT13 cipher, as this is extremely easy to crack. Most grade school kids could break this one in seconds. ;-) If the project that you are working upon has low security needs, (in other words, it's not a financial institution), than you might try something quite basic such as a Vigenere, transposition, or even a playfair. These encryption methodologies are not secure and can be cracked by hackers. Yet, for the average Joe, it will keep them away from the information / data stored inside. One thing that seems to work well is to use to ciphers together. For example, encrypt the data using the playfair cipher -- and then run a transposition cipher. This will erase most of the data signatures that are needed for most hackers to crack the code. At this point, brute force is what most people have to resort upon -- and it's mostly governments that have this ability. ;-) Best wishes! Dusty --- Bjoern Schliessmann wrote: Lie wrote: There is a simple encryption, called ROT13 (Rotate 13). This is very unsecure for any cryptographical purpose, For enhanced security use TROT13 (triple ROT13). but enough to make uninformed user to think it's just a random piece of letters. Security by obscurity doesn't work. If it needs to be protected, protect it well. If it doesn't need to, you don't need to obscure it at all. Regards, Björn -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
In article [EMAIL PROTECTED], Steven D'Aprano [EMAIL PROTECTED] wrote: I really don't recommend the ROT13 cipher, as this is extremely easy to crack. Most grade school kids could break this one in seconds. ;-) I think you missed the point. Any recommendation to use ROT13 is likely to be a joke. A recommendation to use Triple ROT13 is *absolutely* a joke. ROT13 does have a legitimate use, but it's not as a cypher. It is really the equivalent of the newspaper quiz where the answers are upside down at the bottom of the page. By doing this you stop seeing the answers too early. -- David Wild using RISC OS on broadband www.davidhwild.me.uk -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
On Tue, 19 Feb 2008 09:25:52 -0700, Brian wrote: Hi Erik, I really don't recommend the ROT13 cipher, as this is extremely easy to crack. Most grade school kids could break this one in seconds. ;-) I think you missed the point. Any recommendation to use ROT13 is likely to be a joke. A recommendation to use Triple ROT13 is *absolutely* a joke. If the project that you are working upon has low security needs, (in other words, it's not a financial institution), That's rubbish. Do you think that banks are the only companies that care about the security of their data? How would you feel if your doctor accidentally published your medical records onto the Internet, so everybody can see the embarrassing social diseases you've got? (Disclaimer: I don't have any reason to think Brian actually has any embarrassing social diseases, or any other diseases for that matter. I was just making a rhetorical point.) than you might try something quite basic such as a Vigenere, transposition, or even a playfair. These encryption methodologies are not secure and can be cracked by hackers. Yet, for the average Joe, it will keep them away from the information / data stored inside. It's an awful lot of work to do those when it is so simple to call an already existing library that is much stronger. Why do a lot of work to get an insecure result, when you can do a little bit of work to get a secure result? I don't recommend any of these obsolete ciphers except as a learning exercise, or possibly as a challenge: e.g. you *want* people to crack the cipher, but you don't want it too easy for them. One thing that seems to work well is to use to ciphers together. For example, encrypt the data using the playfair cipher -- and then run a transposition cipher. This will erase most of the data signatures that are needed for most hackers to crack the code. At this point, brute force is what most people have to resort upon -- and it's mostly governments that have this ability. ;-) That's absolute rubbish. (1) There are well-understood techniques for breaking all these ciphers, individually or in combination. Often, putting two of them together doesn't make the encryption any harder to break than just using one of them. (2) It's not just governments who can break ciphers by brute force. Anyone can do it. I could probably write a Python function to crack any Caesar cipher in a few minutes, and it would probably run in seconds or minutes. More complex ciphers need more work, but it's certainly feasible: dictionary attacks are simple. Brute force only becomes infeasible when the key is long enough. To brute force a short enough key is within the grasp of *pencil and paper*, if you care enough. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
David H Wild wrote: In article [EMAIL PROTECTED], Steven D'Aprano [EMAIL PROTECTED] wrote: I really don't recommend the ROT13 cipher, as this is extremely easy to crack. Most grade school kids could break this one in seconds. ;-) I think you missed the point. Any recommendation to use ROT13 is likely to be a joke. A recommendation to use Triple ROT13 is *absolutely* a joke. ROT13 does have a legitimate use, but it's not as a cypher. It is really the equivalent of the newspaper quiz where the answers are upside down at the bottom of the page. By doing this you stop seeing the answers too early. Of course, but ROT13 ^ (2n*1) is equivalent to ROT13 for all positive integer n. Hence the confident assertion that A recommendation to use Triple ROT13 is *absolutely* a joke. regards Steve -- Steve Holden+1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
In article [EMAIL PROTECTED], Steve Holden [EMAIL PROTECTED] wrote: Of course, but ROT13 ^ (2n*1) is equivalent to ROT13 for all positive integer n. Why restrict that to positive integers? I believe it works for all integers. But I do think you meant 2n+1, not 2n*1. -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
Roy Smith wrote: In article [EMAIL PROTECTED], Steve Holden [EMAIL PROTECTED] wrote: Of course, but ROT13 ^ (2n*1) is equivalent to ROT13 for all positive integer n. Why restrict that to positive integers? I believe it works for all integers. But I do think you meant 2n+1, not 2n*1. Yes, I did. * and + are much closer in my mind than they are on the keyboard :-) regards Steve -- Steve Holden+1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
On Feb 12, 2:45 am, erikcw [EMAIL PROTECTED] wrote: Hi, I'm trying to devise a scheme to encrypt/obfuscate a short string that basically contains the user's username and record number from the database. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). I'm trying to figure out which approach I should use to encrypt the data. The string will be less than 20 characters long, and I'd like the encrypted version to be about the same size. I tried DES in the Crypto module, but the cipher text was to long to be usable in this case. Any suggestions? Thanks! There is a simple encryption, called ROT13 (Rotate 13). This is very unsecure for any cryptographical purpose, but enough to make uninformed user to think it's just a random piece of letters. The ROT13 is done by adding 13 to each character, so A = N, B = O, C = P, D = Q, etc the neat trick to this encryption is the algorithm is really simple and you don't need a separate decoding algorithm as text == ROT13(ROT13(text)). This algorithm also guarantees that any two different text would have two different ciphertext -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
Lie wrote: There is a simple encryption, called ROT13 (Rotate 13). This is very unsecure for any cryptographical purpose, For enhanced security use TROT13 (triple ROT13). but enough to make uninformed user to think it's just a random piece of letters. Security by obscurity doesn't work. If it needs to be protected, protect it well. If it doesn't need to, you don't need to obscure it at all. Regards, Björn -- BOFH excuse #372: Forced to support NT servers; sysadmins quit. -- http://mail.python.org/mailman/listinfo/python-list
Encrypting a short string?
Hi, I'm trying to devise a scheme to encrypt/obfuscate a short string that basically contains the user's username and record number from the database. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). I'm trying to figure out which approach I should use to encrypt the data. The string will be less than 20 characters long, and I'd like the encrypted version to be about the same size. I tried DES in the Crypto module, but the cipher text was to long to be usable in this case. Any suggestions? Thanks! -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
erikcw [EMAIL PROTECTED] writes: database. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). 1. I hope you're not trying to spam anyone. 2. What happens if the user edits the subject line? I'm trying to figure out which approach I should use to encrypt the data. The string will be less than 20 characters long, and I'd like the encrypted version to be about the same size. Under normal security requirements you cannot do this. The ciphertext has to be longer than the plaintext since you don't want the opponent to be able to tell whether two plaintexts are the same. Therefore you have to attach some random padding to each plaintext. Also, you presumably want the ciphertext to be encoded as printing characters, while normally you'd treat the input as binary, so there is some further expansion. -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
On Feb 11, 4:19 pm, erikcw [EMAIL PROTECTED] wrote: On Feb 11, 4:07 pm, [EMAIL PROTECTED] wrote: erikcw napisal(a): But that can't be reversed, right? I'd like to be able to decrypt the data instead of having to store the hash in my database... In such case it seems you have no choice but to use a symmetric encryption algorithm - in other words, your original method. If the strings are ~20 bytes long (3 DES blocks), then the base64-encoded ciphertext will have 32 characters. In case of AES, that'll be up to 45 characters. Wouldn't such length be acceptable? Paul Rubin napisal(a): 2. What happens if the user edits the subject line? Under normal security requirements you cannot do this. The ciphertext has to be longer than the plaintext since you don't want the opponent to be able to tell whether two plaintexts are the same. Therefore you have to attach some random padding to each plaintext. Also, you presumably want the ciphertext to be encoded as printing characters, while normally you'd treat the input as binary, so there is some further expansion. If what erikcw is looking for is a cryptographically secure protocol, there are more things to be careful about, like authentication or replay attacks. But indeed, I'm wondering now what his use-case is. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). Why not use From field to identify emails from a particular user? Regards, Marek In essence what I'm doing is trying to manage tickets for a helpdesk. I want the ticket identifier to be short enough to fit in the subject line along with the normal subject chosen by the user. So cryptographic security isn't really important. I can't use the from: field because a single user could have multiple tickets. Shouldn't you have a database associating a ticket ID with an email address (among other things)? Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
En Mon, 11 Feb 2008 19:19:00 -0200, erikcw [EMAIL PROTECTED] escribió: In essence what I'm doing is trying to manage tickets for a helpdesk. I want the ticket identifier to be short enough to fit in the subject line along with the normal subject chosen by the user. So cryptographic security isn't really important. I can't use the from: field because a single user could have multiple tickets. And you don't like [bug12345] or even [12345]? To the user, it's a lot clear its purpose, and anybody will understand what you mean if you say Please maintain the bug number in the subject line or similar. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
erikcw napisal(a): But that can't be reversed, right? I'd like to be able to decrypt the data instead of having to store the hash in my database... In such case it seems you have no choice but to use a symmetric encryption algorithm - in other words, your original method. If the strings are ~20 bytes long (3 DES blocks), then the base64-encoded ciphertext will have 32 characters. In case of AES, that'll be up to 45 characters. Wouldn't such length be acceptable? Paul Rubin napisal(a): 2. What happens if the user edits the subject line? Under normal security requirements you cannot do this. The ciphertext has to be longer than the plaintext since you don't want the opponent to be able to tell whether two plaintexts are the same. Therefore you have to attach some random padding to each plaintext. Also, you presumably want the ciphertext to be encoded as printing characters, while normally you'd treat the input as binary, so there is some further expansion. If what erikcw is looking for is a cryptographically secure protocol, there are more things to be careful about, like authentication or replay attacks. But indeed, I'm wondering now what his use-case is. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). Why not use From field to identify emails from a particular user? Regards, Marek -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
On Feb 11, 3:07 pm, [EMAIL PROTECTED] wrote: erikcw napisal(a): Hi, I'm trying to devise a scheme to encrypt/obfuscate a short string that basically contains the user's username and record number from the database. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). I'm trying to figure out which approach I should use to encrypt the data. The string will be less than 20 characters long, and I'd like the encrypted version to be about the same size. I tried DES in the Crypto module, but the cipher text was to long to be usable in this case. Any suggestions? Thanks! How about: hashlib.sha256([EMAIL PROTECTED]|2937267834).hexdigest()[:20] Regards, Marek Thanks Marek, But that can't be reversed, right? I'd like to be able to decrypt the data instead of having to store the hash in my database... -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
erikcw napisal(a): Hi, I'm trying to devise a scheme to encrypt/obfuscate a short string that basically contains the user's username and record number from the database. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). I'm trying to figure out which approach I should use to encrypt the data. The string will be less than 20 characters long, and I'd like the encrypted version to be about the same size. I tried DES in the Crypto module, but the cipher text was to long to be usable in this case. Any suggestions? Thanks! How about: hashlib.sha256([EMAIL PROTECTED]|2937267834).hexdigest()[:20] Regards, Marek -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
Hi, On 2/11/08, erikcw [EMAIL PROTECTED] wrote: In essence what I'm doing is trying to manage tickets for a helpdesk. I want the ticket identifier to be short enough to fit in the subject line along with the normal subject chosen by the user. So cryptographic security isn't really important. I can't use the from: field because a single user could have multiple tickets. I've always wondered why such systems don't use the Message-ID or Reference headers - I know they aren't preserved by all mailers but I think that having this info in the subject line is a) visually disturbing (subjective) b) I guess that the risk of a user modifying the subject line is the same than finding a programm that doesn't to some extent honor the headers i mentioned... flame c) Personally whenever I find a mail that says please keep this in the subject I delete that number on purpose... /flame martin -- http://noneisyours.marcher.name https://twitter.com/MartinMarcher http://www.xing.com/profile/Martin_Marcher http://www.linkedin.com/in/martinmarcher You are not free to read this message, by doing so, you have violated my licence and are required to urinate publicly. Thank you. -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
On Feb 11, 4:07 pm, [EMAIL PROTECTED] wrote: erikcw napisal(a): But that can't be reversed, right? I'd like to be able to decrypt the data instead of having to store the hash in my database... In such case it seems you have no choice but to use a symmetric encryption algorithm - in other words, your original method. If the strings are ~20 bytes long (3 DES blocks), then the base64-encoded ciphertext will have 32 characters. In case of AES, that'll be up to 45 characters. Wouldn't such length be acceptable? Paul Rubin napisal(a): 2. What happens if the user edits the subject line? Under normal security requirements you cannot do this. The ciphertext has to be longer than the plaintext since you don't want the opponent to be able to tell whether two plaintexts are the same. Therefore you have to attach some random padding to each plaintext. Also, you presumably want the ciphertext to be encoded as printing characters, while normally you'd treat the input as binary, so there is some further expansion. If what erikcw is looking for is a cryptographically secure protocol, there are more things to be careful about, like authentication or replay attacks. But indeed, I'm wondering now what his use-case is. I'm using this encrypted string to identify emails from a user. (the string will be in the subject line of the email). Why not use From field to identify emails from a particular user? Regards, Marek In essence what I'm doing is trying to manage tickets for a helpdesk. I want the ticket identifier to be short enough to fit in the subject line along with the normal subject chosen by the user. So cryptographic security isn't really important. I can't use the from: field because a single user could have multiple tickets. -- http://mail.python.org/mailman/listinfo/python-list
Re: Encrypting a short string?
erikcw [EMAIL PROTECTED] writes: In essence what I'm doing is trying to manage tickets for a helpdesk. I want the ticket identifier to be short enough to fit in the subject line along with the normal subject chosen by the user. I think you should use a database to maintain the email addresses since you already have to maintain the contents and history of the help ticket anyway. If the contents of the database is private, then assign the ticket numbers in an unpredictable sequence--I can tell you how to do that cryptographically if you want (I've posted code for it a few times before). That is to stop users from guessing ticket numbers that are valid but belong to other users. If it's a public database (e.g. a bug tracker for a free software project) or if accessing a particular ticket needs a user credential associated with that ticket, then you may as well use sequential numbers. -- http://mail.python.org/mailman/listinfo/python-list
