SQL Server 2014 AES-256加密数据能否在外部手动解密？

Great question! The issue here boils down to two key things: SQL Server adds extra metadata to the output of EncryptByKey, and it uses specific rules to generate the IV and actual encryption key—rules you aren’t accounting for in your online tool setup. Let’s walk through this step by step:

1. The EncryptByKey Output Isn’t Pure Ciphertext #

When you run EncryptByKey, the binary result isn’t just your encrypted data. It’s wrapped with metadata that SQL Server uses internally to validate decryption:

• First 16 bytes: The GUID of the symmetric key you used (to ensure you’re using the right key to decrypt)
• Next 4 bytes: A version marker (always 0x01000000 for AES in SQL Server 2014)
• The rest: Your actual AES-encrypted data (with PKCS#7 padding)

In your example, the encrypted result is:

0x004C1D372DB0FDBE915B16664E37A3DD010000005633680204DCC53BC0CCA8F8ECC9F28A37110E7524A932F2D135CB5E83BCD615CA9DE6EB6F6530E0890990BD0E4377E3

You need to strip off the first 20 bytes to get the pure ciphertext:

0x5633680204DCC53BC0CCA8F8ECC9F28A37110E7524A932F2D135CB5E83BCD615CA9DE6EB6F6530E0890990BD0E4377E3

That’s the value you should input into your online tool as the ciphertext.

2. You’re Using the Wrong IV #

Your IDENTITY_VALUE = 'ffoejkgeifbhkfle' isn’t used directly as the IV. SQL Server takes this string, runs a SHA-1 hash on it, then uses the first 16 bytes of that hash as the AES IV (since AES requires a 128-bit/16-byte IV).

To get the correct IV:

1. Convert the string ffoejkgeifbhkfle to UTF-8 bytes (SQL Server uses the database’s default encoding for non-N-prefixed strings; UTF-8 is standard here)
2. Calculate the SHA-1 hash of those bytes
3. Take the first 16 bytes of the hash result—this is your valid IV

3. Your Key Isn’t the Direct Key_SOURCE Value #

Similarly, the Key_SOURCE = 'fewjgpwgdkfewjgpwgdkfewjgpwgdkfd' isn’t the raw AES-256 key. SQL Server runs a SHA-256 hash on this string, then uses the full 32-byte hash result as the AES-256 key (since AES-256 needs a 256-bit/32-byte key).

To get the correct key:

1. Convert the Key_SOURCE string to UTF-8 bytes
2. Calculate the SHA-256 hash of those bytes—this hash is your AES-256 key

4. Correct Online Tool Settings #

Once you have the pure ciphertext, valid IV, and proper AES key, set up your online tool like this:

• Text: Use the pure ciphertext (strip the 0x prefix if the tool expects raw hex)
• Mode: CBC (SQL Server defaults to AES-CBC for symmetric encryption)
• IV: The 16-byte hex value you generated from the SHA-1 hash of IDENTITY_VALUE
• Key Size: 256 bits
• Key: The 32-byte hex value from the SHA-256 hash of Key_SOURCE
• Padding: PKCS#7 (SQL Server uses PKCS#7 padding, which is compatible with PKCS#5 since AES has a 16-byte block size)

5. Does SQL Server Have Extra Protection? #

No, there’s no secret "extra" encryption here. SQL Server just adds metadata to the encrypted output for internal validation, and uses standard hashing to derive the IV and key from your IDENTITY_VALUE and Key_SOURCE. As long as you correctly extract the ciphertext and generate the right IV/key, you absolutely can decrypt this data externally.

内容的提问来源于stack exchange，提问作者Stev