为了正确理解pdf中标准安全处理程序的操作 我正在尝试从先前加密的pdf重建加密字典的条目/ o / u。 / o和/ u上的加密字典包含：
/P -1852
/CF
<<
/StdCF
<<
/AuthEvent /DocOpen
/Length 16
/CFM/V2
>>
>>
/R 4
/StmF /StdCF
/Filter/Standard
我设法成功重建/ o但我无法重建/ u
主：
public static void main(String[] args) {
String docID;
byte[] userPass=null;
byte[] ownerPass=null;
try {
userPass = userPassString.getBytes("ISO-8859-1");
ownerPass = ownerPassString.getBytes("ISO-8859-1");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
try {
PDDocument doc=PDDocument.load(outPDfDir + "/EncryptedDocument_rc4_128.pdf");
if (doc.isEncrypted()){
EncryptDocument encrypt = new EncryptDocument(userPass,ownerPass,outPDfDir,doc.getEncryptionDictionary().getLength());
encrypt.setRevision(doc.getEncryptionDictionary().getRevision());
encrypt.setVersion(doc.getEncryptionDictionary().getVersion());
COSArray cosArray = doc.getDocument().getDocumentID();
docID=cosArray.getString(0); //only first entry of the array
byte[][] keys = encrypt.computeKeys(userPass, ownerPass, doc.getEncryptionDictionary().getPermissions(), docID.getBytes());
byte[] originalUserKey = doc.getEncryptionDictionary().getUserKey();
byte[] originalownerKey = doc.getEncryptionDictionary().getOwnerKey();
System.out.println(toHex(originalUserKey));
System.out.println(toHex(keys[1]));
if (Arrays.equals(originalUserKey,keys[1])){
System.out.println("User correctly authenticated");
}else{
System.out.println("wrong user password");
}
if (Arrays.equals(originalownerKey,keys[0])){
System.out.println("Owner correctly authenticated");
}else{
System.out.println("wrong user password");
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
加密课程
public class EncryptDocument {
private ARCFour rc4 = new ARCFour();
public static final byte[] ENCRYPT_PADDING = new byte[]{(byte)40, (byte)-65, (byte)78, (byte)94, (byte)78, (byte)117, (byte)-118, (byte)65, (byte)100, (byte)0, (byte)78, (byte)86, (byte)-1, (byte)-6, (byte)1, (byte)8, (byte)46, (byte)46, (byte)0, (byte)-74, (byte)-48, (byte)104, (byte)62, (byte)-128, (byte)47, (byte)12, (byte)-87, (byte)-2, (byte)100, (byte)83, (byte)105, (byte)122};
byte[] userPass;
byte[] ownerPass;
String destPath;
int revision;
int version;
private static final byte[] pad = new byte[]{(byte)40, (byte)-65, (byte)78, (byte)94, (byte)78, (byte)117, (byte)-118, (byte)65, (byte)100, (byte)0, (byte)78, (byte)86, (byte)-1, (byte)-6, (byte)1, (byte)8, (byte)46, (byte)46, (byte)0, (byte)-74, (byte)-48, (byte)104, (byte)62, (byte)-128, (byte)47, (byte)12, (byte)-87, (byte)-2, (byte)100, (byte)83, (byte)105, (byte)122};
private int keyLength;
public EncryptDocument(byte[] userPass, byte[] ownerPass, String destPath,int keylength) {
this.userPass = userPass;
this.ownerPass = ownerPass;
this.destPath = destPath;
this.keyLength=keylength;
}
public byte[][] computeKeys(byte[] userPass, byte[] ownPass, int permissions, byte[] documentId) {
//pad both user and owner pass
byte[] userPad = padPassword(userPass);
byte[] ownerPad = padPassword(ownPass);
byte[][] data = new byte[2][32];
byte[] userKey = new byte[0];
byte[] encryptionKey;
permissions= computePermissions(permissions);
byte[] ownerKey = new byte[0];
try {
ownerKey = computeOwnerKey(userPad, ownerPad);
encryptionKey = computeEncryptionKey(userPad,ownerKey,documentId,permissions);
userKey = computeUserKey(userPad,ownerKey,permissions,documentId,encryptionKey);
} catch (IOException e) {
e.printStackTrace();
}
data[0]=ownerKey;
data[1]=userKey;
return data;
}
private byte[] computeUserKey(byte[] userPad, byte[] ownerKey, int permissions, byte[] documentId, byte[] mkey) throws IOException {
//algorithm 5
byte[] digest;
ByteArrayOutputStream userKey = new ByteArrayOutputStream();
ARCFour rc4 = new ARCFour();
MessageDigest md5 = null;
try {
md5 = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
md5.update(pad); // step b
digest = md5.digest(documentId); //c
//build the input of rc4 encryption
userKey.write(digest);
byte[] iterationKey = new byte[mkey.length];
//encrypt it first time plus other 19 times
for (int i = 0; i < 20; ++i) {
System.arraycopy(mkey, 0, iterationKey, 0, iterationKey.length);
for (int input = 0; input < iterationKey.length; ++input) {
iterationKey[input] = (byte) (iterationKey[input] ^ i);
}
rc4.setKey(iterationKey);
ByteArrayInputStream tmpRes = new ByteArrayInputStream(userKey.toByteArray());
userKey.reset();
rc4.write(tmpRes, userKey);
}
return userKey.toByteArray();
}
private byte[] computeEncryptionKey(byte[] userPad,byte[] ownerKey, byte[] documentId,int permissions){
//initialize hash function
MessageDigest md5 = null;
byte[] encryptedKey =new byte[keyLength / 8];
byte[] digest;
try {
md5 = MessageDigest.getInstance("MD5"); //md5.reset()
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
md5.update(userPad);///pass the padded user password (step b)
md5.update(ownerKey); //pass o entry to the hash function (step c)
byte[] ext = int_to_bb_le(permissions); //new byte[]{(byte)permissions, (byte)(permissions >> 8), (byte)(permissions >> 16), (byte)(permissions >> 24)};
md5.update(ext, 0, 4); //pass permission to the hash function stp d
md5.update(documentId); //pass first element of document id (step e)
if (this.revision>=4)
md5.update(new byte[]{(byte)-1, (byte)-1, (byte)-1, (byte)-1}); //metadata not encryped --> add padding (step f)
digest = md5.digest();
//compute encryption key step g
if(revision == 3 || revision == 4) { //do 50 times step h
for(int k = 0; k < 50; ++k) {
md5.reset();
md5.update(digest,0,keyLength / 8);
digest=md5.digest();
}
}
System.arraycopy(digest, 0, encryptedKey, 0, encryptedKey.length);
return encryptedKey;
}
private byte[] computeOwnerKey(byte[] userPad, byte[] ownerPad) throws IOException {
MessageDigest md5 = null;
ARCFour rc4 = new ARCFour();
try {
md5 = MessageDigest.getInstance("MD5"); //md5.reset()
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
byte[] digest = md5.digest(ownerPad);
byte[] mkey = new byte[this.keyLength / 8];
int i;
for (i = 0; i < 50; ++i) {
md5.update(digest, 0, mkey.length);
System.arraycopy(md5.digest(), 0, digest, 0, mkey.length);
}
//encrypt the padded user password using the result of md5 computation on owner padded password
//revision >3 ==> do it 19 times
ByteArrayOutputStream ownerKey = new ByteArrayOutputStream();
//System.arraycopy(userPad, 0, ownerKey, 0, 32);
rc4.write(new ByteArrayInputStream(userPad), ownerKey);
byte[] iterationKey = new byte[mkey.length];
for (i = 0; i < 20; ++i) {
System.arraycopy(mkey, 0, iterationKey, 0, mkey.length);
//prepare encryption key bitwhise xor between encrypted owner padded password and iteration counter
for (int j = 0; j < iterationKey.length; ++j) {
iterationKey[j] = (byte) (digest[j] ^ i);
}
//encrypt with arc4
rc4.setKey(iterationKey);
ByteArrayInputStream tmpres = new ByteArrayInputStream(ownerKey.toByteArray());
ownerKey.reset();
rc4.write(tmpres, ownerKey);
}
//at the 19 invocation the own key is obtained
return ownerKey.toByteArray();
}
public int computePermissions(int permissions){
permissions |= this.revision != 3 && this.revision != 4 && this.revision != 5?-64:-3904;
permissions &= -4;
return permissions;
}
public byte[] padPassword(byte[] password) {
byte[] userPad = new byte[32];
if(password == null) {
System.arraycopy(pad, 0, userPad, 0, 32);
} else {
System.arraycopy(password, 0, userPad, 0, Math.min(password.length, 32));
if(password.length < 32) {
System.arraycopy(pad, 0, userPad, password.length, 32 - password.length);
}
}
return userPad;
}
public static byte[] int_to_bb_le(int myInteger){
return ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN).putInt(myInteger).allocatelocaterray();
}
}