Package org.syncany.crypto

Class MultiCipherOutputStream

java.lang.Object

java.io.OutputStream

org.syncany.crypto.MultiCipherOutputStream

All Implemented Interfaces:

java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable

public class MultiCipherOutputStream
extends java.io.OutputStream

Implements an output stream that encrypts the underlying output stream using one to many ciphers. Format:

    Length           HMAC'd           Description
    ----------------------------------------------
    04               no               "Sy" 0x02 0x05 (4 bytes)
    01               no               Version (1 byte)
    12               no               HMAC salt             
    01               yes (in header)  Cipher count (=n, 1 byte)
    
    for i := 0..n-1:
      01             yes (in header)  Cipher spec ID (1 byte)
      12             yes (in header)  Salt for cipher i (12 bytes)
      aa             yes (in header)  IV for cipher i (cipher specific length, 0..x)
      
    20               no               Header HMAC (20 bytes, for "HmacSHA1")
    bb               yes (in mode)    Ciphertext (HMAC'd by mode, e.g. GCM)
 

It follows a few Do's and Don'ts: - http://blog.cryptographyengineering.com/2011/11/how-not-to-use-symmetric-encryption.html - http://security.stackexchange.com/questions/30170/after-how-much-data-encryption-aes-256-we-should-change-key Encryption and cipher rules - Don't encrypt with ECB mode (throws exception if ECB is used) - Don't re-use your IVs (IVs are never reused) - Don't encrypt your IVs (IVs are prepended) - Authenticate cipher configuration (algorithm, salts and IVs) - Only use authenticated ciphers

Field Summary

Fields

Modifier and Type	Field	Description
static CipherSpec	HMAC_SPEC
static int	SALT_SIZE
static byte[]	STREAM_MAGIC
static byte	STREAM_VERSION

Constructor Summary

Constructors

Constructor	Description
MultiCipherOutputStream(java.io.OutputStream out, java.util.List<CipherSpec> cipherSpecs, CipherSession cipherSession)

Method Summary

Modifier and Type	Method	Description
void	close()
void	write(byte[] b)
void	write(byte[] b, int off, int len)
void	write(int b)

Methods inherited from class java.io.OutputStream

flush, nullOutputStream

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

STREAM_MAGIC

public static final byte[] STREAM_MAGIC

STREAM_VERSION

public static final byte STREAM_VERSION

See Also:

Constant Field Values

SALT_SIZE

public static final int SALT_SIZE

See Also:

Constant Field Values

HMAC_SPEC

public static final CipherSpec HMAC_SPEC

Constructor Detail

MultiCipherOutputStream

public MultiCipherOutputStream(java.io.OutputStream out,
                               java.util.List<CipherSpec> cipherSpecs,
                               CipherSession cipherSession)
                        throws java.io.IOException

Throws:

java.io.IOException

Method Detail

write

public void write(int b)
           throws java.io.IOException

Specified by:

write in class java.io.OutputStream

Throws:

java.io.IOException

write

public void write(byte[] b)
           throws java.io.IOException

Overrides:

write in class java.io.OutputStream

Throws:

java.io.IOException

write

public void write(byte[] b,
                  int off,
                  int len)
           throws java.io.IOException

Overrides:

write in class java.io.OutputStream

Throws:

java.io.IOException

close

public void close()
           throws java.io.IOException

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Overrides:

close in class java.io.OutputStream

Throws:

java.io.IOException