crypto: Clean up the windows rsa impl (#3611)

Drop the RustCrypto crates for parsing, as windows does indeed provide
parsers. Then switch the error type back to a struct instead of an enum.
Clean up various small helpers.

Author: smalis-msft

support/crypto/Cargo.toml

@@ -78,10 +78,6 @@ windows = { workspace = true, features = [
 ] }
 windows-result.workspace = true
 zerocopy.workspace = true
-# Used by the native BCrypt RSA backend to parse/encode PKCS#8 / PKCS#1.
-der.workspace = true
-pkcs1.workspace = true
-pkcs8 = { workspace = true, features = ["alloc"] }
 
 # Used by the native Security.framework RSA backend to parse/encode PKCS#8 / PKCS#1.
 [target.'cfg(target_os = "macos")'.dependencies]

support/crypto/src/aes_256_gcm/win.rs

@@ -42,7 +42,7 @@ static AES_256_GCM: LazyLock<Result<AlgHandle, Aes256GcmError>> = LazyLock::new(
 });
 
 fn err(err: windows_result::Error, op: &'static str) -> Aes256GcmError {
-    Aes256GcmError(crate::BackendError::Bcrypt(err, op))
+    Aes256GcmError(crate::BackendError(err, op))
 }
 
 pub struct Aes256GcmInner {

support/crypto/src/lib.rs

@@ -42,17 +42,8 @@ pub(crate) struct BackendError(#[source] openssl::error::ErrorStack, &'static st
 /// operation being performed when the error occurred.
 #[cfg(all(native, windows))]
 #[derive(Clone, Debug, thiserror::Error)]
-pub(crate) enum BackendError {
-    /// An error from a BCrypt / CryptoAPI call.
-    #[error("windows crypto error during {1}")]
-    Bcrypt(#[source] windows_result::Error, &'static str),
-    /// An error from encoding or decoding PKCS#8.
-    #[error("PKCS#8 error during {1}")]
-    Pkcs8(#[source] pkcs8::Error, &'static str),
-    /// An error from DER encoding or decoding.
-    #[error("DER error during {1}")]
-    Der(#[source] der::Error, &'static str),
-}
+#[error("windows crypto error during {1}")]
+pub(crate) struct BackendError(#[source] windows_result::Error, &'static str);
 
 /// An error that occurred in the crypto backend, with a description of the
 /// operation being performed when the error occurred.

support/crypto/src/pkcs7/win.rs

@@ -10,7 +10,7 @@ use windows::Win32::Foundation::NTE_BAD_SIGNATURE;
 use windows::Win32::Security::Cryptography::*;
 
 fn err(e: windows_result::Error, op: &'static str) -> Pkcs7Error {
-    Pkcs7Error(crate::BackendError::Bcrypt(e, op))
+    Pkcs7Error(crate::BackendError(e, op))
 }
 
 /// RAII wrapper for HCERTSTORE.