BlowCrypt help and documentation

The suite comprises of programs written in C, C++, perl and tk/tcl.

• blowcrypt
  blowfish (448 bit) 16 rounds
  comprises of blow.cpp,blowfish.h,blowfish.cpp
  usage blowcrypt <0|1> (0=encrypt 1=decrypt)
  

  blowcrypt will send all output to STDOUT

  When encrypting, blowcrypt will pad with zeros to make the file size divisible by sixteen. This is done as blowfish (the algorithm used) is a block cipher and uses 16 bit blocks when encrypting or decrypting Depending on how many padding zeros are added, a range on values from A to Q will be appended to the file to indicate the number of zeros to remove when decrypting.

• md5hash
  md5 hash 128 bit
  comprises of md5c.c
  usage md5hash -s or md5hash
  

  This will create an md5 hash of either a string or a file. It is used during key generation (the key value is hashed to 448 bits by splitting and sending each part to this program). Also this program is used to obtain an md5 hash of a file which is being encrypted. This enables a decrypted file's hash to be compared with the original (and enabling the file to be decrypted correctly)

• remhash
  comprises of remhash.c
  usage remhash

  This will truncate a given file to a new size

• encrypt
  comprises of encrypt (perl script)
  usage encrypt
  

  This program takes a key and gets a 448 bit hash of it. The program then obtains and md5 hash of the file. It then encrypts the file with the hashed key and finally appends the original hash to the file. A new file will replace the file. It will be encrypted and will have the .blowme extension.

• decrypt
  comprises of decryptnew (perl script)
  usage decrypt
  

  This script will hash a given key, obtain the file hash from the end of the file, and decrypt the file. It will then call remhash to remove the last 128 bits of the file (the filehash). The padding zeros will be removed (as specified by the last byte in the file) and a md5 hash will be taken of this new file. If the original file hash and the new file has are identical, then it can be said that the file has decrypted correctly, and the encrypted file will be replaced by a decrpyted file without the .blowme extension.

• tkblow
  comprises of tkblow
  usage tkblow
  

  This is the GUI front end to it all. It allows multiple files to be selected and be encrypted or decrypted with the same key. It calls encrypt and decrypt. It is written in Tk/Tcl and therefore, Tk and Tcl need to be installed on the system for the front end to work.