Java tutorial
package org.bouncycastle.crypto.io; import java.io.FilterInputStream; import java.io.IOException; import java.io.InputStream; import org.bouncycastle.crypto.BufferedBlockCipher; import org.bouncycastle.crypto.InvalidCipherTextException; import org.bouncycastle.crypto.SkippingCipher; import org.bouncycastle.crypto.StreamCipher; import org.bouncycastle.crypto.modes.AEADBlockCipher; import org.bouncycastle.util.Arrays; /** * A CipherInputStream is composed of an InputStream and a cipher so that read() methods return data * that are read in from the underlying InputStream but have been additionally processed by the * Cipher. The cipher must be fully initialized before being used by a CipherInputStream. * <p> * For example, if the Cipher is initialized for decryption, the * CipherInputStream will attempt to read in data and decrypt them, * before returning the decrypted data. */ public class CipherInputStream extends FilterInputStream { private static final int INPUT_BUF_SIZE = 2048; private SkippingCipher skippingCipher; private byte[] inBuf; private BufferedBlockCipher bufferedBlockCipher; private StreamCipher streamCipher; private AEADBlockCipher aeadBlockCipher; private byte[] buf; private byte[] markBuf; private int bufOff; private int maxBuf; private boolean finalized; private long markPosition; private int markBufOff; /** * Constructs a CipherInputStream from an InputStream and a * BufferedBlockCipher. */ public CipherInputStream(InputStream is, BufferedBlockCipher cipher) { this(is, cipher, INPUT_BUF_SIZE); } /** * Constructs a CipherInputStream from an InputStream and a StreamCipher. */ public CipherInputStream(InputStream is, StreamCipher cipher) { this(is, cipher, INPUT_BUF_SIZE); } /** * Constructs a CipherInputStream from an InputStream and an AEADBlockCipher. */ public CipherInputStream(InputStream is, AEADBlockCipher cipher) { this(is, cipher, INPUT_BUF_SIZE); } /** * Constructs a CipherInputStream from an InputStream, a * BufferedBlockCipher, and a specified internal buffer size. */ public CipherInputStream(InputStream is, BufferedBlockCipher cipher, int bufSize) { super(is); this.bufferedBlockCipher = cipher; this.inBuf = new byte[bufSize]; this.skippingCipher = (cipher instanceof SkippingCipher) ? (SkippingCipher) cipher : null; } /** * Constructs a CipherInputStream from an InputStream, a StreamCipher, and a specified internal buffer size. */ public CipherInputStream(InputStream is, StreamCipher cipher, int bufSize) { super(is); this.streamCipher = cipher; this.inBuf = new byte[bufSize]; this.skippingCipher = (cipher instanceof SkippingCipher) ? (SkippingCipher) cipher : null; } /** * Constructs a CipherInputStream from an InputStream, an AEADBlockCipher, and a specified internal buffer size. */ public CipherInputStream(InputStream is, AEADBlockCipher cipher, int bufSize) { super(is); this.aeadBlockCipher = cipher; this.inBuf = new byte[bufSize]; this.skippingCipher = (cipher instanceof SkippingCipher) ? (SkippingCipher) cipher : null; } /** * Read data from underlying stream and process with cipher until end of stream or some data is * available after cipher processing. * * @return -1 to indicate end of stream, or the number of bytes (> 0) available. */ private int nextChunk() throws IOException { if (finalized) { return -1; } bufOff = 0; maxBuf = 0; // Keep reading until EOF or cipher processing produces data while (maxBuf == 0) { int read = in.read(inBuf); if (read == -1) { finaliseCipher(); if (maxBuf == 0) { return -1; } return maxBuf; } try { ensureCapacity(read, false); if (bufferedBlockCipher != null) { maxBuf = bufferedBlockCipher.processBytes(inBuf, 0, read, buf, 0); } else if (aeadBlockCipher != null) { maxBuf = aeadBlockCipher.processBytes(inBuf, 0, read, buf, 0); } else { streamCipher.processBytes(inBuf, 0, read, buf, 0); maxBuf = read; } } catch (Exception e) { throw new CipherIOException("Error processing stream ", e); } } return maxBuf; } private void finaliseCipher() throws IOException { try { finalized = true; ensureCapacity(0, true); if (bufferedBlockCipher != null) { maxBuf = bufferedBlockCipher.doFinal(buf, 0); } else if (aeadBlockCipher != null) { maxBuf = aeadBlockCipher.doFinal(buf, 0); } else { maxBuf = 0; // a stream cipher } } catch (final InvalidCipherTextException e) { throw new InvalidCipherTextIOException("Error finalising cipher", e); } catch (Exception e) { throw new IOException("Error finalising cipher " + e); } } /** * Reads data from the underlying stream and processes it with the cipher until the cipher * outputs data, and returns the next available byte. * <p> * If the underlying stream is exhausted by this call, the cipher will be finalised. * </p> * @throws IOException if there was an error closing the input stream. * @throws InvalidCipherTextIOException if the data read from the stream was invalid ciphertext * (e.g. the cipher is an AEAD cipher and the ciphertext tag check fails). */ public int read() throws IOException { if (bufOff >= maxBuf) { if (nextChunk() < 0) { return -1; } } return buf[bufOff++] & 0xff; } /** * Reads data from the underlying stream and processes it with the cipher until the cipher * outputs data, and then returns up to <code>b.length</code> bytes in the provided array. * <p> * If the underlying stream is exhausted by this call, the cipher will be finalised. * </p> * @param b the buffer into which the data is read. * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no * more data because the end of the stream has been reached. * @throws IOException if there was an error closing the input stream. * @throws InvalidCipherTextIOException if the data read from the stream was invalid ciphertext * (e.g. the cipher is an AEAD cipher and the ciphertext tag check fails). */ public int read(byte[] b) throws IOException { return read(b, 0, b.length); } /** * Reads data from the underlying stream and processes it with the cipher until the cipher * outputs data, and then returns up to <code>len</code> bytes in the provided array. * <p> * If the underlying stream is exhausted by this call, the cipher will be finalised. * </p> * @param b the buffer into which the data is read. * @param off the start offset in the destination array <code>b</code> * @param len the maximum number of bytes read. * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no * more data because the end of the stream has been reached. * @throws IOException if there was an error closing the input stream. * @throws InvalidCipherTextIOException if the data read from the stream was invalid ciphertext * (e.g. the cipher is an AEAD cipher and the ciphertext tag check fails). */ public int read(byte[] b, int off, int len) throws IOException { if (bufOff >= maxBuf) { if (nextChunk() < 0) { return -1; } } int toSupply = Math.min(len, available()); System.arraycopy(buf, bufOff, b, off, toSupply); bufOff += toSupply; return toSupply; } public long skip(long n) throws IOException { if (n <= 0) { return 0; } if (skippingCipher != null) { int avail = available(); if (n <= avail) { bufOff += n; return n; } bufOff = maxBuf; long skip = in.skip(n - avail); long cSkip = skippingCipher.skip(skip); if (skip != cSkip) { throw new IOException("Unable to skip cipher " + skip + " bytes."); } return skip + avail; } else { int skip = (int) Math.min(n, available()); bufOff += skip; return skip; } } public int available() throws IOException { return maxBuf - bufOff; } /** * Ensure the cipher text buffer has space sufficient to accept an upcoming output. * * @param updateSize the size of the pending update. * @param finalOutput <code>true</code> iff this the cipher is to be finalised. */ private void ensureCapacity(int updateSize, boolean finalOutput) { int bufLen = updateSize; if (finalOutput) { if (bufferedBlockCipher != null) { bufLen = bufferedBlockCipher.getOutputSize(updateSize); } else if (aeadBlockCipher != null) { bufLen = aeadBlockCipher.getOutputSize(updateSize); } } else { if (bufferedBlockCipher != null) { bufLen = bufferedBlockCipher.getUpdateOutputSize(updateSize); } else if (aeadBlockCipher != null) { bufLen = aeadBlockCipher.getUpdateOutputSize(updateSize); } } if ((buf == null) || (buf.length < bufLen)) { buf = new byte[bufLen]; } } /** * Closes the underlying input stream and finalises the processing of the data by the cipher. * * @throws IOException if there was an error closing the input stream. * @throws InvalidCipherTextIOException if the data read from the stream was invalid ciphertext * (e.g. the cipher is an AEAD cipher and the ciphertext tag check fails). */ public void close() throws IOException { try { in.close(); } finally { if (!finalized) { // Reset the cipher, discarding any data buffered in it // Errors in cipher finalisation trump I/O error closing input finaliseCipher(); } } maxBuf = bufOff = 0; markBufOff = 0; markPosition = 0; if (markBuf != null) { Arrays.fill(markBuf, (byte) 0); markBuf = null; } if (buf != null) { Arrays.fill(buf, (byte) 0); buf = null; } Arrays.fill(inBuf, (byte) 0); } /** * Mark the current position. * <p> * This method only works if markSupported() returns true - which means the underlying stream supports marking, and the cipher passed * in to this stream's constructor is a SkippingCipher (so capable of being reset to an arbitrary point easily). * </p> * @param readlimit the maximum read ahead required before a reset() may be called. */ public void mark(int readlimit) { in.mark(readlimit); if (skippingCipher != null) { markPosition = skippingCipher.getPosition(); } if (buf != null) { markBuf = new byte[buf.length]; System.arraycopy(buf, 0, markBuf, 0, buf.length); } markBufOff = bufOff; } /** * Reset to the last marked position, if supported. * * @throws IOException if marking not supported by the cipher used, or the underlying stream. */ public void reset() throws IOException { if (skippingCipher == null) { throw new IOException("cipher must implement SkippingCipher to be used with reset()"); } in.reset(); skippingCipher.seekTo(markPosition); if (markBuf != null) { buf = markBuf; } bufOff = markBufOff; } /** * Return true if mark(readlimit) is supported. This will be true if the underlying stream supports marking and the * cipher used is a SkippingCipher, * * @return true if mark(readlimit) supported, false otherwise. */ public boolean markSupported() { if (skippingCipher != null) { return in.markSupported(); } return false; } }