Java 256-bit AES Password-Based Encryption

Question

I need to implement 256 bit AES encryption  but all the examples I have found online use a  KeyGenerator  to generate a 256 bit key  but I would like to use my own passkey  How can I create my own key  I have tried padding it out to 256 bits  but then I get an error saying that the key is too long  I do have the unlimited jurisdiction patch installed  so thats not the problem     Ie  The KeyGenerator looks like this         Get the KeyGenerator KeyGenerator kgen   KeyGenerator getInstance  AES    kgen init 128      192 and 256 bits may not be available     Generate the secret key specs  SecretKey skey   kgen generateKey    byte   raw   skey getEncoded      Code taken from here  EDIT  I was actually padding the password out to 256 bytes  not bits  which is too long  The following is some code I am using now that I have some more experience with this   byte   key   null     TODO byte   input   null     TODO byte   output   null  SecretKeySpec keySpec   null  keySpec   new SecretKeySpec key   AES    Cipher cipher   Cipher getInstance  AES CBC PKCS7Padding    cipher init Cipher ENCRYPT MODE  keySpec   output   cipher doFinal input    The  TODO  bits you need to do yourself  -

User · Answer

Maybe helpful for others with a similar requirement   I had a similar requirement to use AES-256-CBC encrypt and decrypt in Java    To achieve  or specify  the 256-byte encryption decryption  Java Cryptography Extension  JCE  policy should set to  Unlimited   It can be set in the java security file under  JAVA HOME jre lib security  for JDK  or  JAVA HOME lib security  for JRE   crypto policy unlimited  Or in the code as   Security setProperty  crypto policy    unlimited      Java 9 and later versions have this enabled by default

User · Answer

Consider using Encryptor4j of which I am the author   First make sure you have Unlimited Strength Jurisdiction Policy files installed before your proceed so that you can use 256-bit AES keys   Then do the following   String password    mysupersecretpassword    Key key   KeyFactory AES keyFromPassword password toCharArray     Encryptor encryptor   new Encryptor key   AES CBC PKCS7Padding   16     You can now use the encryptor to encrypt your message  You can also perform streaming encryption if you d like  It automatically generates and prepends a secure IV for your convenience   If it s a file that you wish to compress take a look at this answer Encrypting a large file with AES using JAVA for an even simpler approach

User · Answer

What I ve done in the past is hash the key via something like SHA256  then extract the bytes from the hash into the key byte     After you have your byte   you can simply do   SecretKeySpec key   new SecretKeySpec keyBytes   AES    Cipher cipher   Cipher getInstance  AES    cipher init Cipher ENCRYPT MODE  key   byte   encryptedBytes   cipher doFinal clearText getBytes

User · Answer

Generating your own key from a byte array is easy   byte   raw           32 bytes in size for a 256 bit key Key skey   new javax crypto spec SecretKeySpec raw   AES      But creating a 256-bit key isn t enough  If the key generator cannot generate 256-bit keys for you  then the Cipher class probably doesn t support AES 256-bit either  You say you have the unlimited jurisdiction patch installed  so the AES-256 cipher should be supported  but then 256-bit keys should be too  so this might be a configuration problem    Cipher cipher   Cipher getInstance  AES    cipher init Cipher ENCRYPT MODE  skey   byte   encrypted   cipher doFinal plainText getBytes       A workaround for lack of AES-256 support is to take some freely available implementation of AES-256  and use it as a custom provider  This involves creating your own Provider subclass and using it with Cipher getInstance String  Provider   But this can be an involved process

User · Answer

Share the password  a char    and salt  a byte     8 bytes selected by a SecureRandom makes a good salt   which doesn t need to be kept secret  with the recipient out-of-band  Then to derive a good key from this information     Derive the key  given password and salt     SecretKeyFactory factory   SecretKeyFactory getInstance  quot PBKDF2WithHmacSHA256 quot    KeySpec spec   new PBEKeySpec password  salt  65536  256   SecretKey tmp   factory generateSecret spec   SecretKey secret   new SecretKeySpec tmp getEncoded     quot AES quot     The magic numbers  which could be defined as constants somewhere  65536 and 256 are the key derivation iteration count and the key size  respectively  The key derivation function is iterated to require significant computational effort  and that prevents attackers from quickly trying many different passwords  The iteration count can be changed depending on the computing resources available  The key size can be reduced to 128 bits  which is still considered  quot strong quot  encryption  but it doesn t give much of a safety margin if attacks are discovered that weaken AES  Used with a proper block-chaining mode  the same derived key can be used to encrypt many messages  In Cipher Block Chaining  CBC   a random initialization vector  IV  is generated for each message  yielding different cipher text even if the plain text is identical  CBC may not be the most secure mode available to you  see AEAD below   there are many other modes with different security properties  but they all use a similar random input  In any case  the outputs of each encryption operation are the cipher text and the initialization vector     Encrypt the message     Cipher cipher   Cipher getInstance  quot AES CBC PKCS5Padding quot    cipher init Cipher ENCRYPT MODE  secret   AlgorithmParameters params   cipher getParameters    byte   iv   params getParameterSpec IvParameterSpec class  getIV    byte   ciphertext   cipher doFinal  quot Hello  World  quot  getBytes StandardCharsets UTF 8     Store the ciphertext and the iv  On decryption  the SecretKey is regenerated in exactly the same way  using using the password with the same salt and iteration parameters  Initialize the cipher with this key and the initialization vector stored with the message     Decrypt the message  given derived key and initialization vector     Cipher cipher   Cipher getInstance  quot AES CBC PKCS5Padding quot    cipher init Cipher DECRYPT MODE  secret  new IvParameterSpec iv    String plaintext   new String cipher doFinal ciphertext   StandardCharsets UTF 8   System out println plaintext     Java 7 included API support for AEAD cipher modes  and the  quot SunJCE quot  provider included with OpenJDK and Oracle distributions implements these beginning with Java 8  One of these modes is strongly recommended in place of CBC  it will protect the integrity of the data as well as their privacy   A java security InvalidKeyException with the message  quot Illegal key size or default parameters quot  means that the cryptography strength is limited  the unlimited strength jurisdiction policy files are not in the correct location  In a JDK  they should be placed under   jdk  jre lib security Based on the problem description  it sounds like the policy files are not correctly installed  Systems can easily have multiple Java runtimes  double-check to make sure that the correct location is being used

User · Answer

Use this class for encryption  It works   public class ObjectCrypter         public static byte   encrypt byte   ivBytes  byte   keyBytes  byte   mes               throws NoSuchAlgorithmException              NoSuchPaddingException              InvalidKeyException              InvalidAlgorithmParameterException              IllegalBlockSizeException              BadPaddingException  IOException            AlgorithmParameterSpec ivSpec   new IvParameterSpec ivBytes           SecretKeySpec newKey   new SecretKeySpec keyBytes   AES            Cipher cipher   null          cipher   Cipher getInstance  AES CBC PKCS5Padding            cipher init Cipher ENCRYPT MODE  newKey  ivSpec           return  cipher doFinal mes               public static byte   decrypt byte   ivBytes  byte   keyBytes  byte   bytes               throws NoSuchAlgorithmException              NoSuchPaddingException              InvalidKeyException              InvalidAlgorithmParameterException              IllegalBlockSizeException              BadPaddingException  IOException  ClassNotFoundException            AlgorithmParameterSpec ivSpec   new IvParameterSpec ivBytes           SecretKeySpec newKey   new SecretKeySpec keyBytes   AES            Cipher cipher   Cipher getInstance  AES CBC PKCS5Padding            cipher init Cipher DECRYPT MODE  newKey  ivSpec           return  cipher doFinal bytes              And these are ivBytes and a random key   String key    e8ffc7e56311679f12b6fc91aa77a5eb    byte   ivBytes     0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00  0x00    keyBytes   key getBytes  UTF-8

User · Answer

Adding to  Wufoo s edits  the following version uses InputStreams rather than files to make working with a variety of files easier  It also stores the IV and Salt in the beginning of the file  making it so only the password needs to be tracked  Since the IV and Salt do not need to be secret  this makes life a little easier   import java io File  import java io FileInputStream  import java io FileOutputStream  import java io IOException   import java security AlgorithmParameters  import java security InvalidKeyException  import java security NoSuchAlgorithmException  import java security SecureRandom  import java security spec InvalidKeySpecException  import java security spec InvalidParameterSpecException  import java security spec KeySpec   import java util logging Level  import java util logging Logger   import javax crypto BadPaddingException  import javax crypto Cipher  import javax crypto CipherInputStream  import javax crypto IllegalBlockSizeException  import javax crypto NoSuchPaddingException  import javax crypto SecretKey  import javax crypto SecretKeyFactory  import javax crypto spec IvParameterSpec  import javax crypto spec PBEKeySpec  import javax crypto spec SecretKeySpec   public class AES       public final static int SALT LEN       8      static final String     HEXES           0123456789ABCDEF       String                  mPassword      null      byte                    mInitVec       null      byte                    mSalt          new byte SALT LEN       Cipher                  mEcipher       null      Cipher                  mDecipher      null      private final int       KEYLEN BITS    128        see notes below where this is used      private final int       ITERATIONS     65536      private final int       MAX FILE BUF   1024                  create an object with just the passphrase from the user  Don t do anything else yet         param password             public AES String password            mPassword   password             public static String byteToHex byte   raw            if  raw    null                return null                     final StringBuilder hex   new StringBuilder 2   raw length            for  final byte b   raw                hex append HEXES charAt  b  amp  0xF0   gt  gt  4   append HEXES charAt  b  amp  0x0F                        return hex toString               public static byte   hexToByte String hexString            int    len   hexString length            byte   ba    new byte len   2            for  int i   0  i  lt  len  i    2                ba i   2     byte    Character digit hexString charAt i   16   lt  lt  4                                    Character digit hexString charAt i   1   16                       return ba                        debug print messages         param msg             private void Db String msg            System out println     Crypt        msg                         This is where we write out the actual encrypted data to disk using the Cipher created in setupEncrypt           Pass two file objects representing the actual input  cleartext  and output file to be encrypted                there may be a way to write a cleartext header to the encrypted file containing the salt  but I ran        into uncertain problems with that                 param input - the cleartext file to be encrypted         param output - the encrypted data file         throws IOException         throws IllegalBlockSizeException         throws BadPaddingException             public void WriteEncryptedFile InputStream inputStream  OutputStream outputStream              throws IOException  IllegalBlockSizeException  BadPaddingException           try               long             totalread   0              int              nread       0              byte             inbuf       new byte MAX FILE BUF               SecretKeyFactory factory     null              SecretKey        tmp         null                  crate secureRandom salt and store  as member var for later use             mSalt   new byte SALT LEN                SecureRandom rnd   new SecureRandom                 rnd nextBytes mSalt               Db  generated salt      byteToHex mSalt                factory   SecretKeyFactory getInstance  PBKDF2WithHmacSHA1                                    Derive the key  given password and salt                                in order to do 256 bit crypto  you have to muck with the files for Java s  unlimted security                 The end user must also install them  not compiled in  so beware                 see here   http   www javamex com tutorials cryptography unrestricted policy files shtml                             KeySpec spec   new PBEKeySpec mPassword toCharArray    mSalt  ITERATIONS  KEYLEN BITS                tmp   factory generateSecret spec                SecretKey secret   new SecretKeySpec tmp getEncoded     AES                                    Create the Encryption cipher object and store as a member variable                             mEcipher   Cipher getInstance  AES CBC PKCS5Padding                mEcipher init Cipher ENCRYPT MODE  secret                AlgorithmParameters params   mEcipher getParameters                    get the initialization vectory and store as member var             mInitVec   params getParameterSpec IvParameterSpec class  getIV                Db  mInitVec is      byteToHex mInitVec                outputStream write mSalt               outputStream write mInitVec                while   nread   inputStream read inbuf    gt  0                    Db  read     nread     bytes                    totalread    nread                      create a buffer to write with the exact number of bytes read  Otherwise a short read fills inbuf with 0x0                    and results in full blocks of MAX FILE BUF being written                  byte   trimbuf   new byte nread                    for  int i   0  i  lt  nread  i                          trimbuf i    inbuf i                                         encrypt the buffer using the cipher obtained previosly                 byte   tmpBuf   mEcipher update trimbuf                       I don t think this should happen  but just in case                   if  tmpBuf    null                        outputStream write tmpBuf                                                   finalize the encryption since we ve done it in blocks of MAX FILE BUF             byte   finalbuf   mEcipher doFinal                 if  finalbuf    null                    outputStream write finalbuf                              outputStream flush                inputStream close                outputStream close                outputStream close                Db  wrote     totalread     encrypted bytes              catch  InvalidKeyException ex                Logger getLogger AES class getName    log Level SEVERE  null  ex             catch  InvalidParameterSpecException ex                Logger getLogger AES class getName    log Level SEVERE  null  ex             catch  NoSuchAlgorithmException ex                Logger getLogger AES class getName    log Level SEVERE  null  ex             catch  NoSuchPaddingException ex                Logger getLogger AES class getName    log Level SEVERE  null  ex             catch  InvalidKeySpecException ex                Logger getLogger AES class getName    log Level SEVERE  null  ex                                   Read from the encrypted file  input  and turn the cipher back into cleartext  Write the cleartext buffer back out        to disk as  output  File                I left CipherInputStream in here as a test to see if I could mix it with the update   and final   methods of encrypting         and still have a correctly decrypted file in the end  Seems to work so left it in                 param input - File object representing encrypted data on disk         param output - File object of cleartext data to write out after decrypting         throws IllegalBlockSizeException         throws BadPaddingException         throws IOException             public void ReadEncryptedFile InputStream inputStream  OutputStream outputStream              throws IllegalBlockSizeException  BadPaddingException  IOException           try               CipherInputStream cin              long              totalread   0              int               nread       0              byte              inbuf       new byte MAX FILE BUF                   Read the Salt             inputStream read this mSalt               Db  generated salt      byteToHex mSalt                 SecretKeyFactory factory   null              SecretKey        tmp       null              SecretKey        secret    null               factory   SecretKeyFactory getInstance  PBKDF2WithHmacSHA1                 KeySpec spec   new PBEKeySpec mPassword toCharArray    mSalt  ITERATIONS  KEYLEN BITS                tmp      factory generateSecret spec               secret   new SecretKeySpec tmp getEncoded     AES                    Decrypt the message  given derived key and initialization vector                 mDecipher   Cipher getInstance  AES CBC PKCS5Padding                    Set the appropriate size for mInitVec by Generating a New One             AlgorithmParameters params   mDecipher getParameters                 mInitVec   params getParameterSpec IvParameterSpec class  getIV                    Read the old IV from the file to mInitVec now that size is set              inputStream read this mInitVec               Db  mInitVec is      byteToHex mInitVec                mDecipher init Cipher DECRYPT MODE  secret  new IvParameterSpec mInitVec                    creating a decoding stream from the FileInputStream above using the cipher created from setupDecrypt               cin   new CipherInputStream inputStream  mDecipher                while   nread   cin read inbuf    gt  0                    Db  read     nread     bytes                    totalread    nread                      create a buffer to write with the exact number of bytes read  Otherwise a short read fills inbuf with 0x0                 byte   trimbuf   new byte nread                    for  int i   0  i  lt  nread  i                          trimbuf i    inbuf i                                         write out the size-adjusted buffer                 outputStream write trimbuf                              outputStream flush                cin close                inputStream close                outputStream close                Db  wrote     totalread     encrypted bytes              catch  Exception ex                Logger getLogger AES class getName    log Level SEVERE  null  ex                                   adding main   for usage demonstration  With member vars  some of the locals would not be needed             public static void main String   args                create the input txt file in the current directory before continuing         File   input     new File  input txt            File   eoutput   new File  encrypted aes            File   doutput   new File  decrypted txt            String iv        null          String salt      null          AES    en        new AES  mypassword                           write out encrypted file                     try               en WriteEncryptedFile new FileInputStream input   new FileOutputStream eoutput                System out printf  File encrypted to     eoutput getName       niv     iv     nsalt     salt     n n              catch  IllegalBlockSizeException   BadPaddingException   IOException e                e printStackTrace                                     decrypt file                     AES dc   new AES  mypassword                           write out decrypted file                     try               dc ReadEncryptedFile new FileInputStream eoutput   new FileOutputStream doutput                System out println  decryption finished to     doutput getName               catch  IllegalBlockSizeException   BadPaddingException   IOException e                e printStackTrace

User · Answer

After reading through erickson s suggestions  and gleaning what I could from a couple other postings and this example here  I ve attempted to update Doug s code with the recommended changes  Feel free to edit to make it better    Initialization Vector is no longer fixed encryption key is derived using code from erickson 8 byte salt is generated in setupEncrypt   using SecureRandom   decryption key is generated from the encryption salt and password decryption cipher is generated from decryption key and initialization vector removed hex twiddling in lieu of org apache commons codec Hex routines   Some notes  This uses a 128 bit encryption key - java apparently won t do 256 bit encryption out-of-the-box  Implementing 256 requires installing some extra files into the java install directory    Also  I m not a crypto person  Take heed   import java io File  import java io FileInputStream  import java io FileOutputStream  import java io IOException  import java io UnsupportedEncodingException  import java security AlgorithmParameters  import java security InvalidAlgorithmParameterException  import java security InvalidKeyException  import java security NoSuchAlgorithmException  import java security SecureRandom  import java security spec InvalidKeySpecException  import java security spec InvalidParameterSpecException  import java security spec KeySpec   import javax crypto BadPaddingException  import javax crypto Cipher  import javax crypto CipherInputStream  import javax crypto CipherOutputStream  import javax crypto IllegalBlockSizeException  import javax crypto NoSuchPaddingException  import javax crypto SecretKey  import javax crypto SecretKeyFactory  import javax crypto spec IvParameterSpec  import javax crypto spec PBEKeySpec  import javax crypto spec SecretKeySpec   import org apache commons codec DecoderException  import org apache commons codec binary Hex   public class Crypto       String mPassword   null      public final static int SALT LEN   8      byte    mInitVec   null      byte    mSalt   null      Cipher mEcipher   null      Cipher mDecipher   null      private final int KEYLEN BITS   128     see notes below where this is used      private final int ITERATIONS   65536      private final int MAX FILE BUF   1024                  create an object with just the passphrase from the user  Don t do anything else yet          param password             public Crypto  String password                mPassword   password                        return the generated salt for this object         return             public byte    getSalt                  return  mSalt                         return the initialization vector created from setupEncryption         return             public byte    getInitVec                  return  mInitVec                         debug print messages         param msg             private void Db  String msg                System out println      Crypt        msg                         this must be called after creating the initial Crypto object  It creates a salt of SALT LEN bytes        and generates the salt bytes using secureRandom     The encryption secret key is created         along with the initialization vectory  The member variable mEcipher is created to be used        by the class later on when either creating a CipherOutputStream  or encrypting a buffer        to be written to disk                   throws NoSuchAlgorithmException         throws InvalidKeySpecException         throws NoSuchPaddingException         throws InvalidParameterSpecException         throws IllegalBlockSizeException         throws BadPaddingException         throws UnsupportedEncodingException         throws InvalidKeyException             public void setupEncrypt    throws NoSuchAlgorithmException                                                              InvalidKeySpecException                                                              NoSuchPaddingException                                                              InvalidParameterSpecException                                                              IllegalBlockSizeException                                                              BadPaddingException                                                              UnsupportedEncodingException                                                              InvalidKeyException               SecretKeyFactory factory   null          SecretKey tmp   null              crate secureRandom salt and store  as member var for later use          mSalt   new byte  SALT LEN           SecureRandom rnd   new SecureRandom             rnd nextBytes  mSalt           Db   generated salt      Hex encodeHexString  mSalt             factory   SecretKeyFactory getInstance  PBKDF2WithHmacSHA1                Derive the key  given password and salt                          in order to do 256 bit crypto  you have to muck with the files for Java s  unlimted security             The end user must also install them  not compiled in  so beware              see here   http   www javamex com tutorials cryptography unrestricted policy files shtml                     KeySpec spec   new PBEKeySpec  mPassword toCharArray     mSalt  ITERATIONS  KEYLEN BITS           tmp   factory generateSecret  spec           SecretKey secret   new SecretKeySpec  tmp getEncoded     AES                Create the Encryption cipher object and store as a member variable                     mEcipher   Cipher getInstance   AES CBC PKCS5Padding            mEcipher init  Cipher ENCRYPT MODE  secret           AlgorithmParameters params   mEcipher getParameters                 get the initialization vectory and store as member var          mInitVec   params getParameterSpec  IvParameterSpec class  getIV             Db   mInitVec is      Hex encodeHexString  mInitVec                            If a file is being decrypted  we need to know the pasword  the salt and the initialization vector  iv           We have the password from initializing the class  pass the iv and salt here which is        obtained when encrypting the file initially                    param initvec         param salt         throws NoSuchAlgorithmException         throws InvalidKeySpecException         throws NoSuchPaddingException         throws InvalidKeyException         throws InvalidAlgorithmParameterException         throws DecoderException             public void setupDecrypt  String initvec  String salt  throws NoSuchAlgorithmException                                                                                          InvalidKeySpecException                                                                                          NoSuchPaddingException                                                                                          InvalidKeyException                                                                                          InvalidAlgorithmParameterException                                                                                          DecoderException               SecretKeyFactory factory   null          SecretKey tmp   null          SecretKey secret   null              since we pass it as a string of input  convert to a actual byte buffer here         mSalt   Hex decodeHex  salt toCharArray             Db   got salt     Hex encodeHexString  mSalt                get initialization vector from passed string         mInitVec   Hex decodeHex  initvec toCharArray              Db   got initvector      Hex encodeHexString  mInitVec                 Derive the key  given password and salt                in order to do 256 bit crypto  you have to muck with the files for Java s  unlimted security             The end user must also install them  not compiled in  so beware              see here            http   www javamex com tutorials cryptography unrestricted policy files shtml         factory   SecretKeyFactory getInstance  PBKDF2WithHmacSHA1            KeySpec spec   new PBEKeySpec mPassword toCharArray     mSalt  ITERATIONS  KEYLEN BITS            tmp   factory generateSecret spec           secret   new SecretKeySpec tmp getEncoded     AES                Decrypt the message  given derived key and initialization vector             mDecipher   Cipher getInstance  AES CBC PKCS5Padding            mDecipher init Cipher DECRYPT MODE  secret  new IvParameterSpec mInitVec                           This is where we write out the actual encrypted data to disk using the Cipher created in setupEncrypt           Pass two file objects representing the actual input  cleartext  and output file to be encrypted                 there may be a way to write a cleartext header to the encrypted file containing the salt  but I ran        into uncertain problems with that                    param input - the cleartext file to be encrypted         param output - the encrypted data file         throws IOException         throws IllegalBlockSizeException         throws BadPaddingException             public void WriteEncryptedFile  File input  File output  throws                                                                                            IOException                                                                                             IllegalBlockSizeException                                                                                             BadPaddingException               FileInputStream fin          FileOutputStream fout          long totalread   0          int nread   0          byte    inbuf   new byte  MAX FILE BUF            fout   new FileOutputStream  output           fin   new FileInputStream  input            while   nread   fin read  inbuf    gt  0                         Db   read     nread     bytes                totalread    nread                  create a buffer to write with the exact number of bytes read  Otherwise a short read fills inbuf with 0x0                and results in full blocks of MAX FILE BUF being written               byte    trimbuf   new byte  nread               for  int i   0  i  lt  nread  i                    trimbuf i    inbuf i                   encrypt the buffer using the cipher obtained previosly             byte    tmp   mEcipher update  trimbuf                   I don t think this should happen  but just in case               if  tmp    null                  fout write  tmp                         finalize the encryption since we ve done it in blocks of MAX FILE BUF         byte    finalbuf   mEcipher doFinal             if  finalbuf    null              fout write  finalbuf            fout flush            fin close            fout close             Db   wrote     totalread     encrypted bytes                           Read from the encrypted file  input  and turn the cipher back into cleartext  Write the cleartext buffer back out        to disk as  output  File                 I left CipherInputStream in here as a test to see if I could mix it with the update   and final   methods of encrypting         and still have a correctly decrypted file in the end  Seems to work so left it in                   param input - File object representing encrypted data on disk          param output - File object of cleartext data to write out after decrypting         throws IllegalBlockSizeException         throws BadPaddingException         throws IOException             public void ReadEncryptedFile  File input  File output  throws                                                                                                                                              IllegalBlockSizeException                                                                                                                                               BadPaddingException                                                                                                                                               IOException               FileInputStream fin           FileOutputStream fout          CipherInputStream cin          long totalread   0          int nread   0          byte    inbuf   new byte  MAX FILE BUF            fout   new FileOutputStream  output           fin   new FileInputStream  input               creating a decoding stream from the FileInputStream above using the cipher created from setupDecrypt           cin   new CipherInputStream  fin  mDecipher            while   nread   cin read  inbuf    gt  0                         Db   read     nread     bytes                totalread    nread                  create a buffer to write with the exact number of bytes read  Otherwise a short read fills inbuf with 0x0             byte    trimbuf   new byte  nread               for  int i   0  i  lt  nread  i                    trimbuf i    inbuf i                   write out the size-adjusted buffer             fout write  trimbuf                      fout flush            cin close            fin close                    fout close                Db   wrote     totalread     encrypted bytes                           adding main   for usage demonstration  With member vars  some of the locals would not be needed             public static void main String    args                    create the input txt file in the current directory before continuing         File input   new File   input txt            File eoutput   new File   encrypted aes            File doutput   new File   decrypted txt            String iv   null          String salt   null          Crypto en   new Crypto   mypassword                           setup encryption cipher using password  print out iv and salt                     try                   en setupEncrypt               iv   Hex encodeHexString  en getInitVec     toUpperCase               salt   Hex encodeHexString  en getSalt     toUpperCase                   catch  InvalidKeyException e                    e printStackTrace                  catch  NoSuchAlgorithmException e                    e printStackTrace                  catch  InvalidKeySpecException e                    e printStackTrace                  catch  NoSuchPaddingException e                    e printStackTrace                  catch  InvalidParameterSpecException e                    e printStackTrace                  catch  IllegalBlockSizeException e                    e printStackTrace                  catch  BadPaddingException e                    e printStackTrace                  catch  UnsupportedEncodingException e                    e printStackTrace                                   write out encrypted file                     try                   en WriteEncryptedFile  input  eoutput             System out printf   File encrypted to     eoutput getName        niv     iv     nsalt     salt     n n                  catch  IllegalBlockSizeException e                    e printStackTrace                  catch  BadPaddingException e                    e printStackTrace                  catch  IOException e                    e printStackTrace                                    decrypt file                     Crypto dc   new Crypto   mypassword            try                   dc setupDecrypt  iv  salt                 catch  InvalidKeyException e                    e printStackTrace                  catch  NoSuchAlgorithmException e                    e printStackTrace                  catch  InvalidKeySpecException e                    e printStackTrace                  catch  NoSuchPaddingException e                    e printStackTrace                  catch  InvalidAlgorithmParameterException e                    e printStackTrace                  catch  DecoderException e                    e printStackTrace                                   write out decrypted file                     try                   dc ReadEncryptedFile  eoutput  doutput             System out println   decryption finished to     doutput getName                    catch  IllegalBlockSizeException e                    e printStackTrace                  catch  BadPaddingException e                    e printStackTrace                  catch  IOException e                    e printStackTrace

User · Answer

Consider using the Spring Security Crypto Module  The Spring Security Crypto module provides support for symmetric encryption  key generation  and password encoding  The code is distributed as part of the core module but has no dependencies on any other Spring Security  or Spring  code   It s provides a simple abstraction for encryption and seems to match what s required here   The  quot standard quot  encryption method is 256-bit AES using PKCS  5 s PBKDF2  Password-Based Key Derivation Function  2   This method requires Java 6  The password used to generate the SecretKey should be kept in a secure place and not be shared  The salt is used to prevent dictionary attacks against the key in the event your encrypted data is compromised  A 16-byte random initialization vector is also applied so each encrypted message is unique   A look at the internals reveals a structure similar to erickson s answer  As noted in the question  this also requires the Java Cryptography Extension  JCE  Unlimited Strength Jurisdiction Policy  else you ll encounter InvalidKeyException  Illegal Key Size    It s downloadable for Java 6  Java 7 and Java 8  Example usage import org springframework security crypto encrypt Encryptors  import org springframework security crypto encrypt TextEncryptor  import org springframework security crypto keygen KeyGenerators   public class CryptoExample       public static void main String   args            final String password    quot I AM SHERLOCKED quot             final String salt   KeyGenerators string   generateKey                     TextEncryptor encryptor   Encryptors text password  salt                 System out println  quot Salt    quot  quot    salt    quot   quot  quot                     String textToEncrypt    quot  royal secrets  quot           System out println  quot Original text    quot  quot    textToEncrypt    quot   quot  quot                     String encryptedText   encryptor encrypt textToEncrypt           System out println  quot Encrypted text    quot  quot    encryptedText    quot   quot  quot                        Could reuse encryptor but wanted to show reconstructing TextEncryptor         TextEncryptor decryptor   Encryptors text password  salt           String decryptedText   decryptor decrypt encryptedText           System out println  quot Decrypted text    quot  quot    decryptedText    quot   quot  quot                     if textToEncrypt equals decryptedText                 System out println  quot Success  decrypted text matches quot              else               System out println  quot Failed  decrypted text does not match quot                              And sample output   Salt   feacbc02a3a697b0  Original text    royal secrets   Encrypted text   7c73c5a83fa580b5d6f8208768adc931ef3123291ac8bc335a1277a39d256d9a   Decrypted text    royal secrets   Success  decrypted text matches

[java] Java 256-bit AES Password-Based Encryption

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