chore(doc): add a doc page about parameters

tfhe/docs/SUMMARY.md

@@ -32,6 +32,7 @@
   * [Server key](fhe-computation/compute/set-the-server-key.md)
   * [Encryption](fhe-computation/compute/encrypt-data.md)
   * [Decryption](fhe-computation/compute/decrypt-data.md)
+  * [Parameters](fhe-computation/compute/parameters.md)
 * [Data handling](fhe-computation/data-handling/README.md)
   * [Compressing ciphertexts/keys](fhe-computation/data-handling/compress.md)
   * [Serialization/deserialization](fhe-computation/data-handling/serialization.md)

tfhe/docs/fhe-computation/compute/parameters.md

@@ -0,0 +1,59 @@
+# Cryptographic Parameters
+
+The security and efficiency of the FHE algorithms is impacted by the choice of cryptographic parameters.
+
+All parameter sets provide at least 128-bits of security according to the [Lattice-Estimator](https://github.com/malb/lattice-estimator). The recommended parameters for the CPU have an error probability of less than $$2^{-128}$$ when using programmable bootstrapping. This error probability is due to the noisy nature of FHE computations (see [here](../../getting\_started/security\_and\_cryptography.md) for more details about the encryption process).
+
+## Default parameters
+
+When using the high-level API of **TFHE-rs**, you can create a key pair using the default recommended set of parameters with the `Config` object:
+
+```rust
+use tfhe::{ConfigBuilder, generate_keys};
+
+fn main() {
+    let config = ConfigBuilder::default().build();
+
+    // Client-side
+    let (client_key, server_key) = generate_keys(config);
+
+    // encryption and FHE operations
+}
+```
+
+These default parameters may be updated with every new release of **TFHE-rs**. They use blocks of 2 bits of message and 2 bits of carry, a tweaked uniform (TUniform) noise distribution and a $$2^{-128}$$ failure probability for the PBS.
+
+It is possible to override the default parameters with the `with_custom_parameters(block_parameters)` method of the `Config` object. For example, to use a Gaussian distribution instead of the TUniform one you can do:
+
+```rust
+use tfhe::{ConfigBuilder, generate_keys};
+use tfhe::shortint::parameters::v1_0::V1_0_PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
+
+fn main() {
+    let config =
+        ConfigBuilder::with_custom_parameters(V1_0_PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128)
+            .build();
+
+    // Client-side
+    let (client_key, server_key) = generate_keys(config);
+
+    // encryption and FHE operations
+}
+
+```
+
+## Parameters versioning and naming scheme
+
+Parameter sets are versioned for backward compatibility. That way, it is possible to tie the set of parameters to a specific version of **TFHE-rs**, and be confident that the underlying parameters won't change after an upgrade.
+
+The various parameter sets are stored as variables inside the `tfhe::shortint::parameters` module, in submodules named after the versions of **TFHE-rs** where these parameters where added. For example, parameters added in **TFHE-rs** v1.0 can be found inside `tfhe::shortint::parameters::v1_0`.
+
+The names of the parameters give some indications of the capabilities they provide. For example, `tfhe::parameters::v1_0::V1_0_PARAM_MESSAGE_2_CARRY_2_KS_PBS_TUNIFORM_2M128` can be decoded that way:
+- `V1_0`: these parameters were introduced in **TFHE-rs** v1.0
+- `MESSAGE_2`: LWE blocks include 2 bits of message
+- `CARRY_2`: LWE blocks include 2 bits of carry
+- `KS_PBS`: the keyswitch is computed before the bootstrap
+- `TUNIFORM`: the tweaked uniform noise distribution is used
+- `2M128`: the probability of failure for the bootstrap is $$2^{-128}$$
+
+For convenience, aliases are provided for the most used sets of parameters. They are found in the module `tfhe::shortint::parameters::aliases`. Note, however, that these parameters are not stable in time and are always updated to the latest **TFHE-rs** version. For this reason, they should only be used for prototyping and are not suitable for production use cases.

tfhe/src/test_user_docs.rs

@@ -61,6 +61,10 @@ mod test_cpu_doc {
         "../docs/fhe-computation/compute/set-the-server-key.md",
         compute_set_the_server_key
     );
+    doctest!(
+        "../docs/fhe-computation/compute/parameters.md",
+        compute_parameters
+    );
 
     // DATA HANDLING
     doctest!(