file size original size 4 original uncompressed size of the following data decryption info variable decryption information encryption algorithm id algid identifies which of several possible strong encryption algorithms was used for encrypting a file in the zip file the strong encryption algorithms that can be used include but are not limited to aes 3des 2des des rc2 and rc4 the use of other unspecified strong algorithms for encryption is supported by the present invention hash algorithm identifies which of several possible hash algorithms was used for the encryption process for a file in the zip file the algorithms that can be used include but are not limited to md5 sha1 sha512 the use of other unspecified algorithms for hashing is supported by the present invention name value description password_key 0x0001 password is used certificate_key 0x0002 recipient list is used combo_key 0x0003 either a password or a recipient list can be used to decrypt a file double_seed_key 0x0007 both password and recipient list are required to decrypt a file erd is encrypted twice by 2 separate keys double_data_key 0x000f both a password and a recipient list are required to decrypt a file file data is encrypted twice using 2 separate keys master_key_3des 0x4000 specifies 3des algorithm is used for msk a simplified recipient list element is defined as a subset of a recipient list element and is stored to provide redundancy of the recipient list data for the purposes of data recovery.