I don't understand what is input = BINARY FILE output = BINARY FILE or input = TEXT output = TEXT near the source code ?




It indicates what the source code will do with the input file. For example a source code with input = BINARY FILE output = BINARY FILE will encrypt any binary file into a binary format.

Input binary files can contain all types of data: text, image, sound, video … and will open in a word processor or any associated application. Output binary files will contain only pure binary hexadecimal or decimal data, and will not open in a word processor for copying/pasting. Output files contain pure binary data ranging from 0x00 to 0xFF in hexadecimal or 0 to 255 in decimal.


A source code with input = TEXT and output = TEXT will encrypt any text file into a text format.

Let's suppose that you have typed some text in the input window. The encrypted result will be displayed in the output window. This encrypted output can be copied/pasted into a word processor document window or email message window just like any other text.


Let's suppose that you have typed ‘hello’ as text. This ‘hello’ could be encrypted into ‘aplbcffacg’. The exact output will depend on the key (password) used and will contain only letters ranging from ‘a’ to ‘p’, no special characters. It can then be easily copied and pasted into an email message window or a word processor document window.


The main drawback of this method is that the encrypted result in text format is twice as long as the original text or the equivalent encrypted binary format. But the algorithm is the same between the encrypted binary format and the encrypted text format. Only the format of the encrypted result is different.




 I can see on the web algorithms with key length of 512, 1024, 2048 or 4096 bits. Why is PC1 so short with 128 or 256 bit keys ?




You misunderstand the key length problem.

Symmetric algorithms like PC1 are used to encrypt data. They use key lengths of 40, 56, 64, 80, 128 or 256 bits. 256 is the maximum at the present time because there is no need for longer keys. 256 bits will provide maximum security for billions of years.


Asymmetric algorithms like RSA are used to exchange passwords meant for symmetric algorithms when passwords cannot be sent in clear text over the Internet (hackers might intercept the passwords). So asymmetric algorithms are only used to exchange passwords in a secure manner. Only symmetric algorithms are used to encrypt data. Asymmetric algorithms are not used to encrypt data.

Asymmetric algorithms are based on prime numbers and use bigger keys because it’s easier to crack them if the key is too short. Asymmetric length of keys are 512, 1024, 2048 or 4096 bits.




Is PC1 secure ?




PC1 is as secure as other ciphers with same key length. If you use a cipher with a 56 bit key, it’s better than one with a 40 bit key. 256 bit keys are currently the best in security and are likely to remain so for billions of years.

PC1 was originally designed in 1991 with a 80 bit key length. Then PC1 was upgraded to follow the regular increase in the raw computational powers of the machines. PC1 was first upgraded to a 128 bit key length, and then again,  to 256 bit keys.

There is no limit to the key length which could be used with PC1, but it is pointless to use 2300000 bit keys if 256 bit keys will provide absolute security for generations and generations to come.

128 bit keys are the current standard for commercial applications like credit card encryption, data encryption, enterprise interconnection, etc.

256 bit keys are only used for military applications, e.g. to encrypt the launch code of thermonuclear missiles. Military tactical radios and satellite only use 128 bit keys.

Note that a 256 bit key encryption is more time consuming for the processor than a 128 bit key encryption.

PC1 128 bit uses a 16 character password (16*8=128 bits).

PC1 256 bit uses a 32 character password (32*8=256 bits).

When the user’s password is shorter, it can be completed with a fixed string like ‘abcdefghijklm…’ to generate the required 16 or 32 character password.




I want to restrict access to a software through passwords. I want to store encrypted passwords in a database and check out the passwords entered by users against the original database passwords before accepting user connection to my application. I use PC1 256 bit input=text output=text and a fixed key like ‘topsecret’ stored in my software to decrypt the password the user entered and compare it with the password stored in the database.


For example my database contains:


Smith; dfhjedfa

Doe; lbcdlancpd


‘dfhjedfa’ and ‘lbcdlancpd’ are the encrypted forms of the passwords entered by Smith and Doe. When Smith enters ‘toto’ as his literal string password, I decrypt the database ‘dfhjedfa’ string with my fixed ‘topsecret’ key and check that the decrypted result is equal to ‘toto’. If both passwords tally, the user is allowed to connect to my software.


Is this a good method ?




This is a very bad method. Most probably a good hacker could easily disassemble your application. Then he could just as easily find your fixed ‘topsecret’ key  inside your code and he would be able to decrypt all your passwords with it.


You must use one way hash encryption to store passwords in a secure manner, i.e. a user’s password must be encrypted with his own password as a key. No fixed key should ever be used.


Let’s take a few examples:


– Smith with password ‘toto’


You use PC1 to encrypt the ‘toto’ input with the ‘toto’ password as the PC1 key.


Resulting password:


Smith; flokpefh (this is the password to store in your database)


– Doe with password ‘hello’


You use PC1 to encrypt the ‘hello’ input with the ‘hello’ password as the PC1 key.


Resulting password:


Doe; joklnpeomn (this is the password to store in your database)


When Smith tries to connect to your application, he will enter his ‘toto’ password. You then use this ‘toto’ password as the PC1 key and you encrypt this same ‘toto’ input. This will give you ‘flokpefh’ as a resulting password. You can then check this result out against the encrypted password stored in your database. Users are allowed to connect to your application only when both passwords match.


With this method there is no fixed key that a hacker could find stored in your software.

There is no password decryption, only password encryption, and comparison with the encrypted password stored in the database.


However this method offers only mid-level security because someone could steal your database and then know the length of the user’s password.


Let’s take our examples again. Smith’s password as stored in the database is ‘flokpefh’. It is easy to work out that his password is 4 characters long. (length of the encrypted password divided by 2).

Doe’s password as stored in the database is ‘joklnpeomn’. Then his password is 5 characters long.


To avoid such problems, all stored passwords should have the same length. It is recommended to use a 32 byte length.


This is simple to implement. Let’s take our Smith example again.


Smith uses ‘toto’ as a password. Note that users should not be allowed to use passwords of more than 30 characters.


You then generate a string with ‘toto’, plus a fixed string, and the length of the user’s password at position 31 and 32 of the string.


The generated string could be:




– ‘toto’ is the user’s password.


– ‘abcdefghijklmnopqrstuvwxy’ is the fixed string. Note that the length of such fixed strings decreases as the length of the user’s password increases.


– ‘04’ is the length of the user’s password (‘toto’ is 4 characters long). If the password had been ‘hello’ the final 2 digits would have been ‘05’.


The final 2 digits vary from ‘00’ (no password, blank password), to ‘30’ (a password with 30 characters).


Let’s take another example:


‘mysecretpassword’ is the user’s password.


The generated string will be



In this way, the stored string will always be 32 characters long.


Let’s take a look at how one way encryption works:


With our Smith example, you encrypt the ‘totoabcdefghijklmnopqrstuvwxyz04’ data string with PC1 and the ‘toto’ password as the PC1 key. This will give you a 64 byte string to be stored in your database.


With our second example, you encrypt the ‘mysecretpasswordabcdefghijklmn16’ data string with PC1 and the ‘mysecretpassword’ password as the PC1 key. This will give you a 64 byte string to be stored in your database.


Here is how to test if Smith can connect to your application. Let’s suppose that Smith has just entered his ‘toto’ password.


You generate the ‘totoabcdefghijklmnopqrstuvwxyz04’ string, then you encrypt it with the ‘toto’ password as the PC1 key. You will get a 64 byte string that you can compare with the 64 byte string stored in your database. If both match, then you can allow this user to connect to your application.


Hackers could still get hold of your database, but they will neither be able to determine the length of individual passwords, nor what the actual passwords might be.




I have created a word processor and I want to include encryption. I use PC1 256 bits input= BINARY output= BINARY. Can I use PC1 and the password the user will enter to encrypt the user’s documents?




You could, but it would not be the best method because all documents would be encrypted with the same key.


As a rule, a different key should be used for each document. However, most users do not want to memorize so many passwords. The solution is to use a random key to encrypt the document and to encrypt this random key with the user’s password.


So you must first create a random key each time a user wants to encrypt a document.


Let’s suppose that a user has just entered ‘mypassword’ as his document password.


The computer time is 17:23:03, the date 30-01-2004, the mouse position is X:123, Y:087, the free disk space is 128657784668 bytes.


You first reverse the order of the free bytes number. This is because the latter digits of such numbers have the highest renewal rate, i.e. they are most unpredictable. So a ‘128657784668’ free bytes number will be used as ‘866487756821’ in the encryption process.


Then you have to generate a string with all the items that we just mentioned, i.e. time, date, mouse position, free disk space (in reverse order). You will get something like

’17:23:0330-01-200412308786648775’ of which you only take the first 32 bytes.


As a third step, you encrypt the resulting string with the user’s password (‘mypassword’). This will give you a 32 byte binary string (the binary output format is used here).


Here is our example string in hexadecimal:


RESULT KEY = 0DFEFCCD23FDAE121FF77E8F3D5DEEC4CC7876BE3567334839DF478214FE98FF (don’t forget that ‘OD’ or ‘FE’ is only a byte in hexadecimal and doesn’t take two bytes).


You then use this RESULT KEY to encrypt the user’s document with PC1 (input=binary format, output=binary format) into a file.


Next, you encrypt the RESULT KEY with the user’s password (‘mypassword’). Let’s call this encrypted result the ENCRYPTED RESULT KEY.


This ENCRYPTED RESULT KEY must be stored at the start or the end of the final encrypted document.


In this way, each time a user encrypts a different document, the RESULT KEY is different even though the password might be the same (‘mypassword’). This is because the time, date, free disk space and mouse position will be different each time.


Note that ONLY the ENCRYPTED RESULT KEY is stored within the encrypted document. Neither the RESULT KEY, nor the USER’S PASSWORD (‘mypassword’ in our example) should ever be stored within the encrypted document.


This is all for encryption.


Now let’s take a look at how decryption works.


Let’s suppose that our user has just entered his password (‘mypassword’). You read the ENCRYPTED RESULT KEY in the document. You decrypt the ENCRYPTED RESULT KEY with the password the user entered (‘mypassword’), and you get the following RESULT KEY:




You then use this RESULT KEY to decrypt the user’s document.




Ok for encrypting documents with my word processor. But I want to verify if users type the right password or not because I don’t want to show garbage characters on screen when passwords are incorrect. I want to store the user’s password in encrypted form within the encrypted document, then use it to verify if the password the user entered is valid or not.


Can I do this ?




No, you should NEVER store users’ passwords (e.g. ‘mypassword’) within documents, not even in encrypted form.


To check password validity, you must use the following method:


– Add a fixed string at the start of the document like ‘START OF DOCUMENT’.


– Encrypt all the document (even the fixed string) with the RESULT KEY as explained above.


– Encrypt the RESULT KEY with the user’s password and store the ENCRYPTED RESULT KEY at the start of the document.


Now about decryption.


When a user enters a password to decrypt a document, you must use that password to decrypt the ENCRYPTED RESULT KEY, then use the RESULT KEY to decrypt only the first 17 characters of the document. If the first 17 decrypted characters are ‘START OF DOCUMENT’, then the user’s password is valid. If the password is invalid,  you can stop decrypting the document altogether and pop up a message with ‘Your password is incorrect!’




I’m creating a chat system. Two users can exchange messages, files, pictures over the Internet. I want to encrypt all data travelling between the two users. The first user’s application will create a random key like ‘iazskldfhedjuikdeskhfjdkslzopjde’, encrypt this key with PC1 and a fixed key like ‘topsecret’, then send this encrypted key to the other user’s application. The fixed ‘topsecret’ key is stored within the application itself.


The other user’s application will decrypt the encrypted key with the fixed ‘topsecret’ key and then the two applications will use PC1 and the decrypted key ‘iazskldfhedjuikdeskhfjdkslzopjde’ to encrypt/decrypt the data.


Is this a good method ?




No, this is a very bad method because a hacker could easily disassemble your application, then find the fixed ‘topsecret’ key  and he would be able to decrypt all future random key encrypted with the fixed ‘topsecret’ key.


 To securely exchange a key between two users, you should use an asymmetric cipher like PKEP (Pukall Key Exchange Protocol).


The PKEP Phase 1 must be executed at either end of the exchange route on each user’s application. This will create two files, LOCAL.BIN and SEND.BIN, on each user’s application.


Then the SEND.BIN files must be exchanged.


SEND.BIN from User 1 must be sent to User 2 and replace User 2’s SEND.BIN. SEND.BIN from User 2 must be sent to User 1 and replace User 1’s SEND.BIN.


Next, each user must execute PKEP Phase 2.


Each will generate a 32 byte random key. The key will be identical for both User 1 and User 2. Both will also use that key with PC1 to encrypt/decrypt data.




PKEP seems very good but how does it work?




You want mathematics? Ok!


Let’s take a simple example.


Let’s suppose that two users have a common number: 443


User 1 generates a random number: 234

User 2 generates a random number: 718


User 1 computes X= 443*234=103662


Then X is reduced to X modulo 65536 (the rest of the division of 103662/65536)


So X=38126


Then User 1 sends X to User 2


User 2 computes Y=443*718=318074


Then Y is reduced to Y modulo 65536


So Y=55930 (Y is the rest of the division of 318074/65536)


User 2 sends Y to User 1


User 1 computes KEY=Y*234 (234 is User 1’s random number)



KEY=45956 (modulo 65536)


User 2 computes KEY=X*718 (718 is User 2’s random number)



KEY=45956 (modulo 65536)


Now here is some miracle!


KEY at User 1’s end is the same as KEY at User 2’s end.


They can then use this shared key (45956) to encrypt data between them.


PKEP uses the same basic principle but with much bigger numbers. Also PKEP uses the Power operation and not the multiplication between numbers. PKEP is a most secure system.




I’m creating a word processor and I want to protect it with license keys. Users can use the complete version only when they have paid a license fee. I’m using PC1 to create license keys. I take the user’s name and user’s email as a PC1 key and I encrypt a fixed string like ‘WORDPROCESSOR LICENSE’. This generates an encrypted string such as ‘dlpacbndflgkjnhb…..’ I then send these encrypted strings to licensees of my word processor. Users enter these encrypted strings, their name and email.

My word processor then uses their name and email as PC1 key to decrypt the encrypted string. If the result is ‘WORDPROCESSOR LICENSE’, then the application runs in full registered mode and not in shareware mode.


Is it a good method ?




No, this is a very bad method. A hacker could easily disassemble your application and get to know the name and email used to encrypt the fixed key with PC1. Then these hackers could use the same method as yours to produce false license keys. They could use ‘hacker’ and ‘’ as PC1 key to encrypt ‘WORDPROCESSOR LICENSE’ and get a valid license key for your word processor without paying any fee at all.


Here is a safe method to generate license keys:


– First, you should create a random fixed key like ‘aplsdcforfjutikfrpljyhbncvxrztds’.


– You then use that key to encrypt a portion of your application code. (this key is secret and must not be sent to anyone).


For example, let’s suppose that the shareware version of your application can not save documents. The code that saves documents should be encrypted inside your application. In C or Delphi, it’s easier to have this code in a separate .DLL file. When a user wants to save a document, this DLL is called but the code of the DLL itself is encrypted and cannot execute if the user is in shareware version.


– When a user buys a license, you encrypt the random fixed key ‘aplsdcforfjutikfrpljyhbncvxrztds’ with the user’s name, user’s email, user’s address … as PC1 key.


– You then send the encrypted result key like ‘lponmedfgklacbf….’ to the user.


– The user enters the encrypted result key  ‘lponmedfgklacbf….’  in your word processor registration dialog. He also enters his user’s name, user’s email, user’s address.


– Then when the user wants to save a document, the word processor uses the user’s name, user’s email and user’s address to decrypt the encrypted result key ‘lponmedfgklacbf…. and generate the random fixed key ‘aplsdcforfjutikfrpljyhbncvxrztds’. The word processor uses this random fixed key to decrypt the .DLL and call the code inside the .DLL to save the document.


With this method,  no hacker could ever find the random fixed key  ‘aplsdcforfjutikfrpljyhbncvxrztds’ unless they buy a real license key themselves. But to do this, they would have to give their credit card number, their name, their email, their postal address, etc. Hackers do not want to give this kind of information and also do not want to pay for any license. They much prefer to download your application and disassemble it at their home. But by disassembling your application without buying a license key, hackers cannot find your random fixed key because it is not stored within your word processor.


The security lies in the encryption of the .DLL. So you must have a part of your code encrypted in the .DLL itself.


If you only show a message box with ‘Unregistered version’, hackers could patch (modify) your application so that the message box never pops up.


If you use the computer date to allow only 30 days of evaluation, hackers could patch your application to increase the 30 days to 255 days for example. Or they could deactivate the counting of the days and your application would never realize that the date remains the same.


On the contrary, if you use an encrypted .DLL that contains encrypted code, hackers could not alter anything in your application unless they decrypt the .DLL. But to be able to do this, they must first buy a real license and give their personal details, a thing which they’d never want to do.