Add Zirgen-based acceleration

Cargo.toml

@@ -31,6 +31,10 @@ sha1 = { version = "0.10.5", optional = true, default-features = false, features
 sha2 = { version = "0.10.6", optional = true, default-features = false, features = ["oid"] }
 serde = { version = "1.0.184", optional = true, default-features = false, features = ["derive"] }
 
+[target.'cfg(all(target_os = "zkvm", target_arch = "riscv32"))'.dependencies]
+risc0-circuit-bigint = { git = "https://github.com/risc0/risc0", default-features = false, features = [ "bigint-dig-shim" ] }
+risc0-zkvm = { git = "https://github.com/risc0/risc0", default-features = false }
+
 [dev-dependencies]
 base64ct = { version = "1", features = ["alloc"] }
 hex-literal = "0.4.1"
@@ -64,3 +68,8 @@ rustdoc-args = ["--cfg", "docsrs"]
 
 [profile.dev]
 opt-level = 2
+
+# TODO: Point to a version tag once necessary features have stabilized
+[patch.'https://github.com/risc0/risc0.git']
+risc0-circuit-bigint = { git = "https://github.com/risc0/risc0", rev = "e0338f6ce66ac3eba780e045d25df94145a03399" }
+risc0-zkvm = { git = "https://github.com/risc0/risc0", rev = "e0338f6ce66ac3eba780e045d25df94145a03399" }

src/algorithms/rsa.rs

@@ -19,6 +19,15 @@ use crate::traits::{PrivateKeyParts, PublicKeyParts};
 /// or signature scheme. See the [module-level documentation][crate::hazmat] for more information.
 #[inline]
 pub fn rsa_encrypt<K: PublicKeyParts>(key: &K, m: &BigUint) -> Result<BigUint> {
+    #[cfg(all(target_os = "zkvm", target_arch = "riscv32"))]
+    {
+        // If we're in the RISC Zero zkVM, try to use its RSA accelerator circuit
+        if *key.e() == BigUint::new(vec![65537]) {
+            return Ok(risc0_circuit_bigint::rsa::modpow_65537(m, key.n())
+                .expect("Unexpected failure to run RSA accelerator"));
+        }
+        // Fall through when the exponent does not match the accelerator
+    }
     Ok(m.modpow(key.e(), key.n()))
 }
 

src/pkcs1v15/signature.rs

@@ -1,3 +1,4 @@
+#[allow(unused_imports)]
 pub use ::signature::{
     hazmat::{PrehashSigner, PrehashVerifier},
     DigestSigner, DigestVerifier, Error, Keypair, RandomizedDigestSigner, RandomizedSigner, Result,

src/pss/signature.rs

@@ -1,3 +1,4 @@
+#[allow(unused_imports)]
 pub use ::signature::{
     hazmat::{PrehashSigner, PrehashVerifier},
     DigestSigner, DigestVerifier, Error, Keypair, RandomizedDigestSigner, RandomizedSigner, Result,