docs: add config parameters to ecc Book (#1068)

* fix: add config parameters

* fix: toml explanation

* review comments

book/src/custom-extensions/ecc.md

@@ -113,3 +113,20 @@ pub fn main() {
     let p3 = &p1 + &p2;
 }
 ```
+
+### Config parameters
+
+For the guest program to build successfully, all used moduli and curves must be declared in the `.toml` config file in the following format:
+
+```toml
+[app_vm_config.modular]
+supported_modulus = ["115792089237316195423570985008687907853269984665640564039457584007908834671663", "115792089237316195423570985008687907852837564279074904382605163141518161494337"]
+
+[[app_vm_config.ecc.supported_curves]]
+modulus = "115792089237316195423570985008687907853269984665640564039457584007908834671663"
+scalar = "115792089237316195423570985008687907852837564279074904382605163141518161494337"
+a = "0"
+b = "7"
+```
+
+The `supported_modulus` parameter is a list of moduli that the guest program will use. The `ecc.supported_curves` parameter is a list of supported curves that the guest program will use. They must be provided in decimal format in the `.toml` file. For multiple curves create multiple `[[app_vm_config.ecc.supported_curves]]` sections.

extensions/ecc/circuit/src/weierstrass_extension.rs

@@ -27,15 +27,27 @@ use super::{EcAddNeChip, EcDoubleChip};
 #[derive(Clone, Debug, derive_new::new, Serialize, Deserialize)]
 pub struct CurveConfig {
     /// The coordinate modulus of the curve.
+    #[serde(deserialize_with = "deserialize_biguint_from_str")]
     pub modulus: BigUint,
     /// The scalar field modulus of the curve.
+    #[serde(deserialize_with = "deserialize_biguint_from_str")]
     pub scalar: BigUint,
     /// The coefficient a of y^2 = x^3 + ax + b.
+    #[serde(deserialize_with = "deserialize_biguint_from_str")]
     pub a: BigUint,
     /// The coefficient b of y^2 = x^3 + ax + b.
+    #[serde(deserialize_with = "deserialize_biguint_from_str")]
     pub b: BigUint,
 }
 
+fn deserialize_biguint_from_str<'de, D>(deserializer: D) -> Result<BigUint, D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    let s: String = Deserialize::deserialize(deserializer)?;
+    s.parse().map_err(serde::de::Error::custom)
+}
+
 pub static SECP256K1_CONFIG: Lazy<CurveConfig> = Lazy::new(|| CurveConfig {
     modulus: SECP256K1_MODULUS.clone(),
     scalar: SECP256K1_ORDER.clone(),