An implementation of a minimal TPS Service in Rust, in this case implementing ROT13 ciphering.

It goes without saying that ROT13 offers absolutely no security whatsoever. ROT13 is used here to eliminate any focus on the cryptographic aspects of a service.

Messages are defined in CBOR (RFC8949). We use CDDL (RFC8610) to define the allowed message contents. At least some familiarity with CBOR and CDDL is helpful to understand the following.

rot13_service is MIT licensed.

• TPS_GetFeatures_Req: #6.1
• TPS_GetFeatures_Rsp: #6.1
• GPP_ROT13_Encrypt_Req: #6.10
• GPP_ROT13_Encrypt_Rsp: #6.10
• GPP_ROT13_Decrypt_Req: #6.11
• GPP_ROT13_Decrypt_Rsp: #6.11

The underlying implementations of encryption and decryption in ROT13 are identical, as ROT13 is reversible. It thus really doesn't matter which is called as they do the same thing.

Like all TPS Services, it is required to respond to the standard connector message TPS_GetFeatures_Req, returning TPS_GetFeatures_Rsp.

For this service, TPS_GetFeatures_Rsp returns the following:

• svc_name: h'87bae713b08f5e28b9ee4aa6e202440e'
• login_method: [0]
• $$svc_features //= (128 => [0, 1]) // "encrypt" and "decrypt"

GPP_ROT13_Encrypt_Req is encoded in CDDL as follows:

GPP_ROT13_Encrypt_Req = #6.10 ({
  1 => tstr
})

The service responds with GPP_ROT13_Encrypt_Rsp, which is encoded as follows:

GPP_ROT13_Encrypt_Rsp = #6.10 ({
  (1 => tstr / 2 => uint)
})

If map item 1 is present, "encryption" was successful and the tstr contains the "encrypted" payload. If map item 2 is present, "encryption" failed and the uint value provides a helpful error code as follows:

• 1: space character detected
• 2: numeric character detected
• 3: some other symbol detected
• 4: message was too large to process

As this crate is intended to be able to be used in environments that do not support allocators, we use fixed length buffers. In this code, the largest string that can be encoded is 255 characters.

GPP_ROT13_Decrypt_Req is encoded in CDDL as follows:

GPP_ROT13_Decrypt_Req = #6.11 ({
  1 => tstr
})

The service responds with GPP_ROT13_Encrypt_Rsp, which is encoded as follows:

 GPP_ROT13_Decrypt_Rsp = #6.11 ({
   (1 => tstr / 2 => uint)
})

If map item 1 is present, "decryption" was successful and the tstr contains the "decrypted" payload. If map item 2 is present, "decryption" failed and the uint value provides a helpful error code as follows:

• 1: space character detected
• 2: numeric character detected
• 3: some other symbol detected
• 4: message was too large to process

There are test cases covering the operation of the service.