A Rust library for the recovered FairPlay page-key algorithm and AES-128-CBC decryption of protected executable regions. It has no IPA, bundle, filesystem, Mach-O or device dependencies. The caller supplies the region and metadata.

use fairplay::{Decryptor, PageRecords, PAGE_SIZE};

fn decrypt_selected_region(
    credential: &[u8; 16],
    sinf: &[u8],
    supf: &[u8],
    original_file_offset: u64,
    encrypted_region: &mut [u8],
) -> Result<usize, Box<dyn std::error::Error>> {
    let decoder = Decryptor::from_sinf(credential, sinf)?;
    let records = PageRecords::from_supf(supf, 0x0100000c, 0)?;
    let first_page = u32::try_from(original_file_offset / PAGE_SIZE as u64)?;
    Ok(decoder.decrypt_region_in_place(encrypted_region, first_page, records)?)
}

Cache a Decryptor for binaries sharing a SINF. from_sinf_fields accepts an already parsed SinfFields { name, iviv, private }; from_work_key accepts the recovered 16-byte masked working key directly. A working key differs from the saved credential and from an individual page AES key.

PageRecords::from_bytes borrows flat 32-byte records from an existing SUPF parser. from_supf provides optional metadata parsing and selects an exact CPU type/subtype; it supports SUPF 3/5 and tags 507/510/612. SINF decoding handles both 440-byte and 448-byte private records. No code parses the executable.

Caller responsibilities #

Pass only the protected region, containing a nonzero whole number of 4096-byte pages. Decryption resets CBC with each record's IV and removes no padding. Extra SUPF records are allowed.
Compute the first absolute page index from the original complete executable offset. For a FAT binary this includes the architecture slice's file base: (slice_base + cryptoff) / 4096. Do not reset it to zero for a section or slice.
Match the SUPF architecture and record range to the selected region. Records start at the beginning of the protected region. For a later subregion, advance both first_page_index and the record range via records.slice(start..end).
Clear the executable's encryption flag only after decryption succeeds, and handle bundle metadata, signing and output publication in the consuming code.

For page-at-a-time or parallel processing, PageRecords::get provides a PageRecord for decrypt_page_in_place. derive_page_key is available when another component owns CBC decryption. The decoder can be shared across threads.

Region decryption allocates no buffers. Size, record count and page-index validation happens before mutation. Those checks do not authenticate page ciphertext: the recovered scheme uses CBC without an authentication tag. The SINF private record's markers detect credentials that fail its decoding check. Secrets are omitted from Debug and temporary SINF keys/plaintext and AES key schedules use zeroization.