org.apache.poi.poifs.crypt
Class CryptoFunctions

java.lang.Object
  org.apache.poi.poifs.crypt.CryptoFunctions

@Internal
public class CryptoFunctions
extends java.lang.Object

Helper functions used for standard and agile encryption

CryptoFunctions

public CryptoFunctions()

hashPassword

public static byte[] hashPassword(java.lang.String password,
                                  HashAlgorithm hashAlgorithm,
                                  byte[] salt,
                                  int spinCount)

2.3.4.7 ECMA-376 Document Encryption Key Generation (Standard Encryption)
2.3.4.11 Encryption Key Generation (Agile Encryption)

The encryption key for ECMA-376 document encryption [ECMA-376] using agile encryption MUST be generated by using the following method, which is derived from PKCS #5: Password-Based Cryptography Version 2.0 [RFC2898].

Let H() be a hashing algorithm as determined by the PasswordKeyEncryptor.hashAlgorithm element, H_n be the hash data of the n-th iteration, and a plus sign (+) represent concatenation. The password MUST be provided as an array of Unicode characters. Limitations on the length of the password and the characters used by the password are implementation-dependent. The initial password hash is generated as follows:

H_0 = H(salt + password)

The salt used MUST be generated randomly. The salt MUST be stored in the PasswordKeyEncryptor.saltValue element contained within the \EncryptionInfo stream as specified in section 2.3.4.10. The hash is then iterated by using the following approach:

H_n = H(iterator + H_n-1)

where iterator is an unsigned 32-bit value that is initially set to 0x00000000 and then incremented monotonically on each iteration until PasswordKey.spinCount iterations have been performed. The value of iterator on the last iteration MUST be one less than PasswordKey.spinCount.

For POI, H_final will be calculated by generateKey(byte[],HashAlgorithm,byte[],int)

Parameters:

password -

hashAlgorithm -

salt -

spinCount -

Returns:

the hashed password

hashPassword

public static byte[] hashPassword(java.lang.String password,
                                  HashAlgorithm hashAlgorithm,
                                  byte[] salt,
                                  int spinCount,
                                  boolean iteratorFirst)

Generalized method for read and write protection hash generation. The difference is, read protection uses the order iterator then hash in the hash loop, whereas write protection uses first the last hash value and then the current iterator value

Parameters:

password -

hashAlgorithm -

salt -

spinCount -

iteratorFirst - if true, the iterator is hashed before the n-1 hash value, if false the n-1 hash value is applied first

Returns:

the hashed password

generateIv

public static byte[] generateIv(HashAlgorithm hashAlgorithm,
                                byte[] salt,
                                byte[] blockKey,
                                int blockSize)

2.3.4.12 Initialization Vector Generation (Agile Encryption)

Initialization vectors are used in all cases for agile encryption. An initialization vector MUST be generated by using the following method, where H() is a hash function that MUST be the same as specified in section 2.3.4.11 and a plus sign (+) represents concatenation:

• If a blockKey is provided, let IV be a hash of the KeySalt and the following value:
  blockKey: IV = H(KeySalt + blockKey)
• If a blockKey is not provided, let IV be equal to the following value:
  KeySalt:IV = KeySalt
• If the number of bytes in the value of IV is less than the the value of the blockSize attribute corresponding to the cipherAlgorithm attribute, pad the array of bytes by appending 0x36 until the array is blockSize bytes. If the array of bytes is larger than blockSize bytes, truncate the array to blockSize bytes.

generateKey

public static byte[] generateKey(byte[] passwordHash,
                                 HashAlgorithm hashAlgorithm,
                                 byte[] blockKey,
                                 int keySize)

2.3.4.11 Encryption Key Generation (Agile Encryption)

The final hash data that is used for an encryption key is then generated by using the following method:

H_final = H(H_n + blockKey)

where blockKey represents an array of bytes used to prevent two different blocks from encrypting to the same cipher text.

If the size of the resulting H_final is smaller than that of PasswordKeyEncryptor.keyBits, the key MUST be padded by appending bytes with a value of 0x36. If the hash value is larger in size than PasswordKeyEncryptor.keyBits, the key is obtained by truncating the hash value.

Parameters:

passwordHash -

hashAlgorithm -

blockKey -

keySize -

Returns:

intermediate key

getCipher

public static javax.crypto.Cipher getCipher(javax.crypto.SecretKey key,
                                            CipherAlgorithm cipherAlgorithm,
                                            ChainingMode chain,
                                            byte[] vec,
                                            int cipherMode)

Initialize a new cipher object with the given cipher properties and no padding If the given algorithm is not implemented in the JCE, it will try to load it from the bouncy castle provider.

Parameters:

key - the secret key

cipherAlgorithm - the cipher algorithm

chain - the chaining mode

vec - the initialization vector (IV), can be null

cipherMode - Cipher.DECRYPT_MODE or Cipher.ENCRYPT_MODE

Returns:

the requested cipher

Throws:

java.security.GeneralSecurityException

EncryptedDocumentException - if the initialization failed or if an algorithm was specified, which depends on a missing bouncy castle provider

getCipher

public static javax.crypto.Cipher getCipher(java.security.Key key,
                                            CipherAlgorithm cipherAlgorithm,
                                            ChainingMode chain,
                                            byte[] vec,
                                            int cipherMode,
                                            java.lang.String padding)

Initialize a new cipher object with the given cipher properties If the given algorithm is not implemented in the JCE, it will try to load it from the bouncy castle provider.

Parameters:

key - the secret key

cipherAlgorithm - the cipher algorithm

chain - the chaining mode

vec - the initialization vector (IV), can be null

cipherMode - Cipher.DECRYPT_MODE or Cipher.ENCRYPT_MODE

padding - the padding (null = NOPADDING, ANSIX923Padding, PKCS5Padding, PKCS7Padding, ISO10126Padding, ...)

Returns:

the requested cipher

Throws:

java.security.GeneralSecurityException

EncryptedDocumentException - if the initialization failed or if an algorithm was specified, which depends on a missing bouncy castle provider

getBlock0

public static byte[] getBlock0(byte[] hash,
                               int size)

Returns a new byte array with a truncated to the given size. If the hash has less then size bytes, it will be filled with 0-bytes

Parameters:

hash - the to be truncated/filled hash byte array

size - the size of the returned byte array

Returns:

the padded hash

getMessageDigest

public static java.security.MessageDigest getMessageDigest(HashAlgorithm hashAlgorithm)

getMac

public static javax.crypto.Mac getMac(HashAlgorithm hashAlgorithm)

registerBouncyCastle

public static void registerBouncyCastle()

createXorVerifier1

public static int createXorVerifier1(java.lang.String password)

Create the verifier for xor obfuscation (method 1)

Parameters:

password - the password

Returns:

the verifier (actually a short value)

See Also:

2.3.7.1 Binary Document Password Verifier Derivation Method 1, 2.3.7.4 Binary Document Password Verifier Derivation Method 2, Part 4 - Markup Language Reference - Ecma International - 3.2.12 fileSharing

createXorVerifier2

public static int createXorVerifier2(java.lang.String password)

This method generates the xor verifier for word documents < 2007 (method 2). Its output will be used as password input for the newer word generations which utilize a real hashing algorithm like sha1.

Parameters:

password - the password

Returns:

the hashed password

See Also:

2.3.7.4 Binary Document Password Verifier Derivation Method 2, How to set the editing restrictions in Word using Open XML SDK 2.0, Funny: How the new powerful cryptography implemented in Word 2007 turns it into a perfect tool for document password removal.

xorHashPassword

public static java.lang.String xorHashPassword(java.lang.String password)

This method generates the xored-hashed password for word documents < 2007.

xorHashPasswordReversed

public static java.lang.String xorHashPasswordReversed(java.lang.String password)

Convenience function which returns the reversed xored-hashed password for further processing in word documents 2007 and newer, which utilize a real hashing algorithm like sha1.

createXorKey1

public static int createXorKey1(java.lang.String password)

Create the xor key for xor obfuscation, which is used to create the xor array (method 1)

Parameters:

password - the password

Returns:

the xor key

See Also:

2.3.7.2 Binary Document XOR Array Initialization Method 1, 2.3.7.4 Binary Document Password Verifier Derivation Method 2

createXorArray1

public static byte[] createXorArray1(java.lang.String password)

Creates an byte array for xor obfuscation (method 1)

Parameters:

password - the password

Returns:

the byte array for xor obfuscation

See Also:

2.3.7.2 Binary Document XOR Array Initialization Method 1, Libre Office implementation