Encrypt and decrypt a String in java

Question

I am new to cryptography  I wish to learn how to encrypt and decrypt the text in a file    when I refer the related articles in net  I had a doubt that whether the encrypted text will be same for single text when encryption is done multiple times on the same text  Can anyone please clear my doubt

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I had a doubt that whether the encrypted text will be same for single text when encryption done by multiple times on a same text??

This depends strongly on the crypto algorithm you use:

One goal of some/most (mature) algorithms is that the encrypted text is different when encryption done twice. One reason to do this is, that an attacker how known the plain and the encrypted text is not able to calculate the key.
Other algorithm (mainly one way crypto hashes) like MD5 or SHA based on the fact, that the hashed text is the same for each encryption/hash.

User · Answer

public String encrypt String str            try                  Encode the string into bytes using utf-8             byte   utf8   str getBytes  UTF8                    Encrypt             byte   enc   ecipher doFinal utf8                   Encode bytes to base64 to get a string             return new sun misc BASE64Encoder   encode enc             catch  javax crypto BadPaddingException e              catch  IllegalBlockSizeException e              catch  UnsupportedEncodingException e              catch  java io IOException e                      return null             public String decrypt String str            try                  Decode base64 to get bytes             byte   dec   new sun misc BASE64Decoder   decodeBuffer str                   Decrypt             byte   utf8   dcipher doFinal dec                   Decode using utf-8             return new String utf8   UTF8              catch  javax crypto BadPaddingException e              catch  IllegalBlockSizeException e              catch  UnsupportedEncodingException e              catch  java io IOException e                      return null            Here s an example that uses the class    try          Generate a temporary key  In practice  you would save this key         See also Encrypting with DES Using a Pass Phrase      SecretKey key   KeyGenerator getInstance  DES   generateKey            Create encrypter decrypter class     DesEncrypter encrypter   new DesEncrypter key           Encrypt     String encrypted   encrypter encrypt  Don t tell anybody             Decrypt     String decrypted   encrypter decrypt encrypted     catch  Exception e

User · Answer

Whether encrypted be the same when plain text is encrypted with the same key depends of algorithm and protocol. In cryptography there is initialization vector IV: http://en.wikipedia.org/wiki/Initialization_vector that used with various ciphers makes that the same plain text encrypted with the same key gives various cipher texts.

I advice you to read more about cryptography on Wikipedia, Bruce Schneier http://www.schneier.com/books.html and "Beginning Cryptography with Java" by David Hook. The last book is full of examples of usage of http://www.bouncycastle.org library.

If you are interested in cryptography the there is CrypTool: http://www.cryptool.org/ CrypTool is a free, open-source e-learning application, used worldwide in the implementation and analysis of cryptographic algorithms.

[java] Encrypt and decrypt a String in java

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