Update bigint2 impl with 4096 bit support (#4)

* update acceleration to use latest version of bigint2 (with 4096 bit support)

* bump version

* bump to 1.2

Cargo.toml

@@ -32,7 +32,7 @@ sha2 = { version = "0.10.6", optional = true, default-features = false, features
 serde = { version = "1.0.184", optional = true, default-features = false, features = ["derive"] }
 
 [target.'cfg(target_os = "zkvm")'.dependencies]
-risc0-bigint2 = { git = "https://github.com/risc0/risc0", rev = "8fc8437633f08a66e0fbacce947f41d01b074774", default-features = false, features = ["num-bigint-dig"] }
+risc0-bigint2 = { version = "1.2.0", default-features = false, features = ["num-bigint-dig", "unstable"] }
 
 [dev-dependencies]
 base64ct = { version = "1", features = ["alloc"] }

src/algorithms/rsa.rs

@@ -21,9 +21,14 @@ use crate::traits::{PrivateKeyParts, PublicKeyParts};
 pub fn rsa_encrypt<K: PublicKeyParts>(key: &K, m: &BigUint) -> Result<BigUint> {
     #[cfg(target_os = "zkvm")]
     {
+        use risc0_bigint2::ToBigInt2Buffer;
         // If we're in the RISC Zero zkVM, try to use an accelerated version.
         if *key.e() == BigUint::new(vec![65537]) {
-            return Ok(risc0_bigint2::rsa::modpow_65537(m, key.n()));
+            let m = m.to_u32_array();
+            let n = key.n().to_u32_array();
+            let mut result = [0u32; 128];
+            risc0_bigint2::rsa::modpow_65537(&m, &n, &mut result);
+            return Ok(BigUint::from_u32_array(result));
         }
         // Fall through when the exponent does not match the accelerator
     }