Provide RFC 3394 default IV explicitly for AES key wrap

openssl 0.10.80 enforces that any cipher with a defined IV must have one
supplied explicitly — passing `None` panics at runtime with
"an IV is required for this cipher" inside `Crypter::new` / `decrypt`
(see openssl-rs/symm.rs around the IV-required check).

The two call sites here are in the RFC 6637 OpenPGP key-wrap helpers and
both go through AES Key Wrap (RFC 3394). RFC 3394 §2.2.3.1 defines the
"default initial value" for the wrap function as the constant
`A6A6A6A6A6A6A6A6`, used when no Alternative Initial Value is supplied.

Pass that constant explicitly so the cipher contract is satisfied without
changing the wire-level behaviour (the byte stream produced/consumed on
the network is identical to what older openssl versions did when `None`
was passed).

Reproduces with the export-findmy tool against any CloudKit zone that
returns PCS-encrypted records (e.g. the FindMy BeaconStore zone) when
built against current openssl crate releases.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: gregakespret

src/util.rs

@@ -1588,7 +1588,7 @@ pub fn rfc6637_wrap_key<T: HasPublic>(public_key: &CompactECKey<T>, key: &[u8],
         *i = padding_count as u8;
     }
 
-    let mut c = Crypter::new(Cipher::from_nid(Nid::ID_AES128_WRAP).unwrap(), Mode::Encrypt, &aes_key[..16], None)?;
+    let mut c = Crypter::new(Cipher::from_nid(Nid::ID_AES128_WRAP).unwrap(), Mode::Encrypt, &aes_key[..16], Some(&[0xa6u8; 8]))?;
     let mut out = vec![0u8; message.len() + 16];
 
     let mut count = c.update(&message, &mut out)?;
@@ -1618,7 +1618,7 @@ pub fn rfc6637_unwrap_key(private_key: &CompactECKey<Private>, wrapped_key: &[u8
     // RFC6637 KDF
     let hash = rfc6637_kdf(fingerprint, &secret);
 
-    let unwrapped = decrypt(Cipher::from_nid(Nid::ID_AES128_WRAP).unwrap(), &hash[..16], None, &unpacked.wrapped)?;
+    let unwrapped = decrypt(Cipher::from_nid(Nid::ID_AES128_WRAP).unwrap(), &hash[..16], Some(&[0xa6u8; 8]), &unpacked.wrapped)?;
 
     let padding_len = *unwrapped.last().unwrap() as usize;
     for i in 0..padding_len {