mirror of https://github.com/yeka/zip.git
55 lines
2.4 KiB
Plaintext
55 lines
2.4 KiB
Plaintext
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This is a fork of the Go archive/zip package to add support
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for reading password protected AES encrypted files. Only supports
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Winzip's AES extension: http://www.winzip.com/aes_info.htm. This
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package DOES NOT intend to implement the encryption methods
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mentioned in the original PKWARE spec (sections 6.0 and 7.0):
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https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
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WinZip AES specifies
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====================================================================
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1. Encryption-Decryption w/ AES-CTR (128, 192, or 256 bits)
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2. Key generation with PBKDF2-HMAC-SHA1 (1000 iteration count) that
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generates a master key broken into the following:
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a. First m bytes is for the encryption key
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b. Next n bytes is for the authentication key
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c. Last 2 bytes is the password verification value.
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3. Following salt lengths are used w/ password during keygen:
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------------------------------
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AES Key Size | Salt Size
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------------------------------
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128bit(16bytes) | 8 bytes
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192bit(24bytes) | 12 bytes
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256bit(32bytes) | 16 bytes
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-------------------------------
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4. Master key len = AESKeyLen + AuthKeyLen + PWVLen:
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a. AES 128 = 16 + 16 + 2 = 34 bytes of key material
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b. AES 192 = 24 + 24 + 2 = 50 bytes of key material
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c. AES 256 = 32 + 32 + 2 = 66 bytes of key material
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5. Authentication Key is same size as AES key.
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6. Authentication with HMAC-SHA1-80 (truncated to 80bits).
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7. A new master key is generated for every file.
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8. The file header and directory header compression method will
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be 99 (decimal). The actual compression method will be in the
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extra's payload at the end of the directory header.
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9. A extra field will be added to the file header and directory
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header identified by 0x9901 and contains the following info:
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a. Header ID (2 bytes)
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b. Data Size (2 bytes)
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c. Vendor Version (2 bytes)
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d. Vendor ID (2 bytes)
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e. AES Strength (1 byte)
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f. Compression Method (2 bytes)
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10. The Data Size is always 7.
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11. The Vendor Version can either be 0x0001 (AE-1) or
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0x0002 (AE-2).
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12. Vendor ID is ASCII "AE"
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13. AES Strength:
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a. 0x01 - AES-128
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b. 0x02 - AES-192
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c. 0x03 - AES-256
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14. Compression Method is the actual compression method
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used that was replaced by the encryption process.
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15. AE-1 keeps the CRC and should be verified after decompression.
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16. AE-2 removes the CRC and shouldn't be verified after decompression.
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Refer to http://www.winzip.com/aes_info.htm#winzip11 for the reasoning.
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