AES-128-WRAP-PAD-INV ENCRYPTION TOOL

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The AES-128-WRAP-PAD-INV algorithm is a cryptographic procedure used for secure key unwrapping in accordance with the Advanced Encryption Standard (AES) specifications. It operates on 128-bit keys and applies a padding mechanism to ensure the integrity of wrapped data. This algorithm is specifically designed to reverse the AES key wrapping with padding process, recovering the original key material from an encrypted and padded input.

Input Requirements

The algorithm requires an input consisting of a wrapped key block along with an initial key encryption key (KEK) of 128 bits. The input key block may include padding added during the wrapping process to align the data to the required block size. Correct input formatting is crucial for successful unwrapping.

Core Procedure

The core steps of AES-128-WRAP-PAD-INV include:

Initialization: The algorithm sets up the AES cipher in ECB mode using the 128-bit KEK. It also determines the length of the input wrapped key and identifies any padding bytes appended during the wrapping process.
Iterative Unwrapping: The wrapped key is divided into 64-bit blocks. The algorithm iteratively decrypts these blocks in a specific order, reversing the sequence used during key wrapping. Each iteration applies AES decryption while adjusting intermediate results to remove the effect of previous encryption rounds.
Padding Verification: After unwrapping, the algorithm examines the last byte of the decrypted output to determine the padding length. It validates that all padding bytes are consistent with the PKCS#7 padding standard, ensuring data integrity and correctness.
Key Reconstruction: Once padding is verified, the algorithm reconstructs the original key from the decrypted blocks. It removes padding bytes and concatenates the intermediate decrypted blocks to restore the full-length original key material.

Output

The output of AES-128-WRAP-PAD-INV is the original unwrapped key, free from padding and fully restored to its original size. Any failure in padding verification or block decryption will result in an error, indicating that the wrapped input may have been tampered with or corrupted.

Security Considerations

This algorithm provides strong security for key unwrapping by leveraging AES-128 encryption and strict padding verification. It is essential to ensure that the KEK remains confidential, as its compromise would allow unauthorized access to the wrapped key material. Implementation must prevent side-channel leaks during the iterative decryption process to maintain robustness against timing and cache-based attacks.

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