deprecate use of GenericArray

[lthiery]

With const generics, it should be possible now. I think we use GenericArray because it impls Default though. I'm not sure what we need to use instead @lulf

eg:

let mut phy: DataPayloadCreator<[u8; 255], C> = DataPayloadCreator::default();
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `core::default::Default` is not implemented for `[u8; 255]`

[plaes]

Firstly, GenericArray dependency is used both in our code and our dependencies, whenever default-crypto is used.

Our unconditional usage

• JoinAcceptCreator.encrypt_payload(...):

  lora-rs/lorawan-encoding/src/creator.rs

  Lines 175 to 179 in 969ee24

  	for i in 0..(d.len() >> 4) {
  	let start = (i << 4) + 1;
  	let tmp = GenericArray::from_mut_slice(&mut d[start..(16 + start)]);
  	aes_enc.decrypt_block(tmp);
  	}

• We use it in securityhelpers::encrypt_frm_data_payload(...):
  

  lora-rs/lorawan-encoding/src/securityhelpers.rs

  Line 61 in 969ee24

  let s_block = GenericArray::from_mut_slice(&mut s[..]);

• We re-export generic_array from securityhelpers: https://github.com/lora-rs/lora-rs/
  blob/969ee2406d957954921d4be6fda69adac976534b/lorawan-encoding/src/securityhelpers.rs#L2

Internal re-export usage

• EncryptedJoinAcceptPayload.decrypt(...):

  lora-rs/lorawan-encoding/src/parser.rs

  Lines 378 to 379 in 969ee24

  	let block = GenericArray::from_mut_slice(&mut bytes[start..(start + 16)]);
  	aes_enc.encrypt_block(block);

• Encrypter, Decrypter and Keys traits:

  lora-rs/lorawan-encoding/src/keys.rs

  Lines 187 to 201 in 969ee24

  	pub trait Encrypter {
  	fn encrypt_block(&self, block: &mut GenericArray<u8, U16>);
  	}
  	/// Trait for implementations of AES128 decryption.
  	pub trait Decrypter {
  	fn decrypt_block(&self, block: &mut GenericArray<u8, U16>);
  	}
  	/// Trait for implementations of CMAC.
  	pub trait Mac {
  	fn input(&mut self, data: &[u8]);
  	fn reset(&mut self);
  	fn result(self) -> GenericArray<u8, U16>;
  	}

Use by dependencies

Regarding dependencies, RustCrypto (from where our aes and cmac implementations are coming from) is trying to get rid of GenericArray dependency as well in favor of const generics - RustCrypto/traits#1481

As an interim step they have introduced a hybrid_array crate and have ported latest release candidate version to use it instead of GenericArray.
Relevant PRs:

• Migrate to hybrid-array; MSRV 1.65 RustCrypto/utils#944
• crypto-common: migrate to hybrid-array; MSRV 1.65 RustCrypto/traits#1319
• cipher+digest: migrate to hybrid array; MSRV 1.65 RustCrypto/traits#1358

[plaes]

I have a quick and dirty (with only minimal changes to get it to build) branch here that uses the pre-release crates: https://github.com/plaes/lora-rs/tree/hybrid-array