Ho to decrypt data in Objective c

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C

Objective-C

1. get keyData from iCloud
2. wrappedOffset = keyDataSize - (ECP_LEN + WRAPPED_KEY_LEN)
3. get wrappedKey (at wrappedOffset)
4. get CLASS_KEY
iOS 5/6: ((UINT32*)(keyData + wrappedOffset))[-1]
iOS 7: ((UINT32*)(keyData + wrappedOffset))[-3]
5. decrypt wrappedKey using CLASS_KEY
6. get AES_KEY from wrappedKey
7. file decryption: by 0x1000 blocks (unique IV for every block)

i have key data and file.
can you guide me in decryption. in Objective c language