Attachment 24106 Details for Bug 47652 – src/java/org/apache/poi/hssf/record/RC4Header.java

src/java/org/apache/poi/hssf/record/RC4Header.java

RC4Header.java (text/x-java), 4.01 KB, created by Maxim Valyanskiy on 2009-08-06 02:58:22 UTC

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Creator: Maxim Valyanskiy

Created: 2009-08-06 02:58:22 UTC

Size: 4.01 KB

patch

obsolete

>package org.apache.poi.hssf.record;
>
>import javax.crypto.Cipher;
>import javax.crypto.SecretKey;
>import javax.crypto.spec.SecretKeySpec;
>import java.io.UnsupportedEncodingException;
>import java.security.GeneralSecurityException;
>import java.security.InvalidKeyException;
>import java.security.MessageDigest;
>import java.util.Arrays;
>
>/*
>Implementation based on
>[MS-OFFCRYPTO] â v20090708
>Office Document Cryptography Structure Specification
> */
>public class RC4Header {
>    private final byte[] salt = new byte[16];
>    private final byte[] encryptedVerifier = new byte[16];
>    private final byte[] encryptedVerifierHash = new byte[16];
>
>    private final Cipher rc4;
>    private final MessageDigest md5;
>
>    /*
>        Excel uses encryption when you choose certain "protection" settings even without
>        a password. In this case the password used is "VelvetSweatshop", but Excel will
>        try that automatically instead of prompting for a password.
>    */
>    private static final String FIXED_PASSWORD = "VelvetSweatshop";
>    private static String password = FIXED_PASSWORD;
>
>    public static final int BLOCK_SIZE = 1024;
>
>    public RC4Header(RecordInputStream in) {
>        int minor = in.readShort();
>
>        if (minor!=1) {
>            throw new RecordFormatException("Unexpected VersionInfo number for RC4Header");
>        }
>
>        in.readFully(salt, 0, 16);
>        in.readFully(encryptedVerifier, 0, 16);
>        in.readFully(encryptedVerifierHash, 0, 16);
>
>        try {
>            rc4 = Cipher.getInstance("RC4");
>            md5 = MessageDigest.getInstance("MD5");
>
>            SecretKey key = getKey(password, 0);
>
>            if (!verifyKey(key)) {
>                throw new RecordFormatException("Document encrypted, need password");
>            }
>        } catch (GeneralSecurityException e) {
>            throw new RecordFormatException("Can't create RC4 cipher", e);
>        }
>    }
>
>    private SecretKey getKey(String password, int blockNumber) {
>        try {
>            byte[] h0 = md5.digest(password.getBytes("UTF-16LE"));
>
>            byte[] truncatedHash = Arrays.copyOf(h0, 5);
>            byte[] intermediateBuffer = new byte[336];
>
>            for (int i=0; i<16; i++) {
>                System.arraycopy(truncatedHash, 0, intermediateBuffer, i*21, 5);
>                System.arraycopy(salt, 0, intermediateBuffer, i*21+5, 16);
>            }
>
>            byte[] h1 = md5.digest(intermediateBuffer);
>
>            byte[] key = Arrays.copyOf(h1, 5);
>
>            byte[] finalData = new byte[5+4];
>
>            System.arraycopy(key, 0, finalData, 0, 5);
>
>            byte[] block = new byte[4];
>            block[0] = (byte) (blockNumber & 0xFF);
>            block[1] = (byte) ((blockNumber >> 8) & 0xFF);
>            block[2] = (byte) ((blockNumber >> 16) & 0xFF);
>            block[3] = (byte) ((blockNumber >> 24) & 0xFF);
>
>            System.arraycopy(block, 0, finalData, 5, 4);
>
>            byte[] hFinal = md5.digest(finalData);
>
>            byte[] encryptionKey = Arrays.copyOf(hFinal, 16);
>
>            return new SecretKeySpec(encryptionKey, "RC4");
>        } catch (UnsupportedEncodingException e) {
>            throw new RuntimeException(e); // can't happen
>        }
>    }
>
>    private boolean verifyKey(SecretKey key) throws InvalidKeyException {
>        rc4.init(Cipher.DECRYPT_MODE, key);
>        byte[] verifier = rc4.update(encryptedVerifier);
>        byte[] verifierHash = rc4.update(encryptedVerifierHash);
>
>        byte[] expectedVerifierHash = md5.digest(verifier);
>
>        return Arrays.equals(expectedVerifierHash, verifierHash);
>    }
>
>    public Cipher createCypher(int blockNumber) {
>        SecretKey key = getKey(password, blockNumber);
>        try {
>            rc4.init(Cipher.DECRYPT_MODE, key);
>        } catch (InvalidKeyException e) {
>            throw new RuntimeException(e);
>        }
>
>        return rc4;
>    }
>
>    public static void setPassword(String password) {
>        if (password==null) {
>            RC4Header.password = FIXED_PASSWORD;
>        } else {
>            RC4Header.password = password;
>        }
>    }
>}

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Attachments on bug 47652: 24105 | 24106 | 24107 | 24108 | 24136