Function handle_aead_decrypt 

pub fn handle_aead_decrypt(
    process: &ProcessorState<'_>,
) -> Result<Vec<AdviceMutation>, EventError>

Event handler for AEAD decryption.

This handler is called when the VM emits an AEAD_DECRYPT_EVENT. It reads the full ciphertext (including padding block) and tag from memory, performs decryption and tag verification using AEAD-Poseidon2, then pushes the plaintext onto the advice stack.

Process:

1. Reads full ciphertext from memory at src_ptr ((num_blocks + 1) * 8 elements)
2. Reads authentication tag from memory at src_ptr + (num_blocks + 1) * 8
3. Constructs EncryptedData and decrypts using AEAD-Poseidon2
4. Extracts only the data blocks (first num_blocks * 8 elements) from plaintext
5. Pushes the data blocks (WITHOUT padding) onto the advice stack in reverse order

Memory layout at src_ptr:

• [ciphertext_blocks(num_blocks * 8), encrypted_padding(8), tag(4)]
• This handler reads ALL elements: data blocks + padding + tag

The MASM decrypt procedure will then:

1. Load the plaintext data blocks from advice stack and write to dst_ptr using adv_pipe
2. Call encrypt which reads the data blocks and adds padding automatically
3. Re-encrypt data + padding to compute authentication tag
4. Compare computed tag with expected tag and halt if they don’t match

Non-determinism soundness: Using advice for decryption is cryptographically sound because:

1. The MASM procedure re-verifies the tag when decrypting
2. The deterministic encryption creates a bijection between plaintext and ciphertext
3. A malicious prover cannot provide incorrect plaintext without causing tag mismatch