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# Lua bindings for libopaque
These bindings provide access to libopaque which implements the
[IRTF CFRG RFC draft](https://github.com/cfrg/draft-irtf-cfrg-opaque)
or you can read the [original paper](https://eprint.iacr.org/2018/163).
## Dependencies
These bindings depend on the following:
- libopaque: https://github.com/stef/libopaque/
- libsodium
## Building
You need to have libopaque installed, and working (thus also libsodium), then:
```
make
```
## Examples
see test.lua
## API
There is one data structure that is used by libopaque:
### `Ids`
The IDs of the client (idU) and the server (idS) are passed directly
as seperate parameters to functions that need to handle IDs.
## 1-step registration
1-step registration is only specified in the original paper. It is not
specified by the IRTF CFRG draft. 1-step registration has the benefit
that the supplied password (`pwd`) can be checked on the server for
password rules (e.g., occurrence in common password lists, please obey
[NIST SP
800-63-3b](https://pages.nist.gov/800-63-3/sp800-63b.html#memsecret)). It
has the drawback that the password is exposed to the server.
```lua
rec, export_key = register(pwd, skS, idU, idS);
```
The function expects these paramters:
- `pwd` is the user's password.
- `skS` is an optional explicitly specified server long-term key
- `idU` is the clients ID,
- `idS` is the servers ID,
This function returns:
- `rec` should be stored by the server associated with the ID of the user.
- `export_key` is an extra secret that can be used to encrypt
additional data that you might want to store on the server next to
your record.
## 4-step registration
Registration as specified in the IRTF CFRG draft consists of the
following 4 steps:
### Step 1: The user creates a registration request.
```lua
sec, req = createRegistrationReq(pwd);
```
- `pwd` is the user's password.
The user should hold on to `sec` securely until step 3 of the
registration process. `req` needs to be passed to the server running
step 2.
### Step 2: The server responds to the registration request.
```lua
sec, resp = createRegistrationResp(req, skS);
```
- `req` comes from the user running the previous step.
- `skS` is an optional explicitly specified server long-term private key
The server should hold onto `sec` securely until step 4 of the registration process.
`resp` should be passed to the user running step 3.
### Step 3: The user finalizes the registration using the response from the server.
```lua
rec, export_key = finalizeReq(sec, resp, idU, idS);
```
- `sec` contains sensitive data and should be disposed securely after usage in this step.
- `resp` comes from the server running the previous step.
- `idU` is the clients ID,
- `idS` is the servers ID,
The function outputs:
- `rec` should be passed to the server running step 4.
- `export_key` is an extra secret that can be used to encrypt
additional data that you might want to store on the server next to
your record.
### Step 4: The server finalizes the user's record.
```lua
rec = storeRec(sec, rec);
```
or alternatively with explicitly specified long-term server private key:
```lua
rec = store1kRec(sec, skS, rec);
```
- `rec` comes from the client running the previous step.
- `skS` is an explicitly specified server long-term key
- `sec` contains sensitive data and should be disposed securely after usage in this step.
The function returns:
- `rec` should be stored by the server associated with the ID of the user.
**Important Note**: Confusingly this function is called `StoreUserRecord`, yet it
does not do any storage. How you want to store the record (`rec`) is up
to the implementor using this API.
## Establishing an opaque session
After a user has registered with a server, the user can initiate the
AKE and thus request its credentials in the following 3(+1)-step protocol:
### Step 1: The user initiates a credential request.
```lua
sec, req = createCredentialReq(pwd)
```
- `pwd` is the user's password.
The user should hold onto `sec` securely until step 3 of the protocol.
`pub` needs to be passed to the server running step 2.
### Step 2: The server responds to the credential request.
```lua
resp, sk, sec = createCredentialResp(req, rec, cfg, idU, idS, infos);
```
- `req` comes from the user running the previous step.
- `rec` is the user's record stored by the server at the end of the registration protocol.
- `context` is a string distinguishing this instantiation of the protocol from others, e.g. "MyApp-v0.2"
- `idU` is the clients ID,
- `idS` is the servers ID,
This function returns:
- `resp` needs to be passed to the user running step 3.
- `sk` is a shared secret, the result of the AKE.
- `sec` is the servers sensitive context. The server should hold onto
this values ecurely until the optional step 4 of the protocol, if
needed. otherwise this value should be discarded securely.
### Step 3: The user recovers its credentials from the server's response.
```lua
sk, authU, export_key = recoverCredentials(resp, sec, context, idU, idS);
```
- `resp` comes from the server running the previous step.
- `sec` contains the client sensitive data from the first step and
should be disposed securely after this step.
- `context` is a string distinguishing this instantiation of the protocol from others, e.g. "MyApp-v0.2"
- `idU` is the client ID.
- `idS` is the server ID.
This function returns:
- `sk` is a shared secret, the result of the AKE.
- `authU` is an authentication tag that can be passed in step 4 for
explicit user authentication.
- `export_key` can be used to decrypt additional data stored by the server.
### Step 4 (Optional): The server authenticates the user.
This step is only needed if there is no encrypted channel setup
towards the server using the shared secret.
```lua
userAuth(sec, authU);
```
- `sec` contains the servers sensitive context from the second step
and should be disposed securely after usage in this step.
- `authU` comes from the user running the previous step.
The function returns a boolean `false` in case the authentication
failed, otherwise `true`.
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