Add pure Rust crypto crates for hashing/HMAC and encryption

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "snmp2"
-version = "0.4.14"
+version = "0.4.15"
 edition = "2021"
 description = "SNMP v1/v2/v3 sync/async client library with traps and MIB support"
 authors = ["Serhij S. <div@altertech.com>"]
@@ -21,12 +21,29 @@ snmptools = { version = "^0.1.2", optional = true }
 tokio = { version = "1.47", features = ["net"], optional = true }
 openssl = { version = "0.10", optional = true }
 
+md-5 = { version = "0.10", optional = true }
+sha1 = { version = "0.10", optional = true }
+digest = { version = "0.10", optional = true }
+sha2 = { version = "0.10", optional = true }
+aes = { version = "0.8", optional = true }
+cipher = { version = "0.4", optional = true }
+des = { version = "0.8", optional = true }
+hmac = { version = "0.12", optional = true }
+cbc = { version = "0.1", optional = true }
+cfb-mode = { version = "0.8", optional = true }
+rand = { version = "0.9", optional = true }
+
 [dev-dependencies]
-tokio = { version = "=1.47" }
+tokio = { version = "1" }
 
 [features]
+default = ["tokio", "v3_rust"]
+
 mibs = ["dep:snmptools"]
 tokio = ["dep:tokio"]
-v3 = ["openssl"]
+v3 = []
 heap_buffers = []
-full = ["mibs", "tokio", "v3"]
+full = ["mibs", "tokio", "v3_rust"]
+
+v3_openssl = ["v3", "openssl"]
+v3_rust = ["v3", "md-5", "sha1", "digest", "sha2", "aes", "cipher", "des", "hmac", "cbc", "cfb-mode", "rand"]

README.md

@@ -36,7 +36,7 @@ Supports:
 - Synchronous/Asynchronous requests
 - UDP transport
 - MIBs (with `mibs` feature, requires `libnetsnmp`)
-- SNMP v3 (requires `v3` feature)
+- SNMP v3 (enable `v3_openssl` or `v3_rust` feature)
 
 # Examples
 
@@ -139,7 +139,7 @@ let socket = UdpSocket::bind("0.0.0.0:1161").unwrap();
 socket.send_to(&bytes, target_addr).unwrap();
 ```
 
-### With SNMPv3 (requires `v3` feature)
+### With SNMPv3 (enable `v3_openssl` or `v3_rust`)
 
 When using SNMPv3, you need to provide the security context to convert the PDU to bytes:
 
@@ -210,9 +210,13 @@ assert_eq!(snmp_oid, snmp_oid2);
 
 # SNMPv3
 
-- Requires `v3` crate feature.
+- Requires enabling one of the features: `v3_openssl` or `v3_rust`.
+  - `v3_openssl`: uses OpenSSL for hashing/HMAC and symmetric encryption.
+  - `v3_rust`: uses pure Rust crypto crates for hashing/HMAC and encryption.
 
-- All cryptographic algorithms are provided by [openssl](https://www.openssl.org/).
+- Cryptographic algorithms are provided by the selected backend:
+  - `v3_openssl`: [openssl](https://www.openssl.org/)
+  - `v3_rust`: pure Rust crates [Rust Crypto](https://github.com/RustCrypto): (`md-5`, `sha1`, `sha2`, `hmac`, `aes`, `des`, etc.)
 
 - For authentication, supports: MD5 (RFC3414), SHA1 (RFC3414) and non-standard
   SHA224, SHA256, SHA384, SHA512.
@@ -221,8 +225,22 @@ assert_eq!(snmp_oid, snmp_oid2);
   AES192-CFB, AES256-CFB. Additional/different AES modes are not supported and
   may require patching the crate.
 
-Note: DES legacy encryption may be disabled in openssl by default or even not
-supported at all. Refer to the library documentation how to enable it.
+Note: For `v3_openssl`, DES legacy encryption may be disabled in OpenSSL by default
+or not supported at all. Refer to the library documentation how to enable it.
+
+### Feature selection examples
+
+Pure Rust backend:
+
+```shell
+cargo add snmp2 --features v3_rust
+```
+
+OpenSSL backend (Windows-friendly vendored build):
+
+```shell
+cargo add snmp2 --features "v3_openssl,openssl/vendored"
+```
 
 ## Example
 
@@ -261,21 +279,22 @@ loop {
 }
 ```
 
-## Building
+## Building (`v3_openssl`)
 
-In case of problems (e.g. with [cross-rs](https://github.com/cross-rs/cross)),
-add `openssl` with `vendored` feature:
+When using the `v3_openssl` backend, in case of problems (e.g. with
+[cross-rs](https://github.com/cross-rs/cross)), add `openssl` with `vendored` feature:
 
 ```shell
 cargo add openssl --features vendored
 ```
 
-## FIPS-140 support
+## FIPS-140 support (`v3_openssl`)
 
-The crate uses openssl cryptography only and becomes FIPS-140 compliant as soon
+When using the `v3_openssl` backend, the crate becomes FIPS-140 compliant as soon
 as FIPS mode is activated in `openssl`. Refer to the
 [openssl crate](https://docs.rs/openssl) crate and
 [openssl library](https://www.openssl.org/) documentation for more details.
+The `v3_rust` backend does not rely on OpenSSL and is not FIPS-certified.
 
 ## MSRV
 

build.rs

@@ -0,0 +1,15 @@
+fn main() {
+    let has_v3 = std::env::var("CARGO_FEATURE_V3").is_ok();
+    let has_v3_openssl = std::env::var("CARGO_FEATURE_V3_OPENSSL").is_ok();
+    let has_v3_rust = std::env::var("CARGO_FEATURE_V3_RUST").is_ok();
+
+    match (has_v3_openssl, has_v3_rust) {
+        (true, false) | (false, true) => {} // OK
+        (true, true) => panic!("feature_v3_openssl and feature_v3_rust are mutually exclusive!"),
+        (false, false) => {
+            if has_v3 {
+                panic!("feature_v3_openssl or feature_v3_rust is required")
+            }
+        }
+    }
+}

src/lib.rs

@@ -12,7 +12,7 @@ pub mod snmp;
 mod syncsession;
 #[cfg(feature = "v3")]
 pub mod v3;
-#[cfg(feature = "v3")]
+#[cfg(feature = "v3_openssl")]
 pub use openssl;
 pub use syncsession::SyncSession;
 #[cfg(feature = "tokio")]
@@ -141,7 +141,7 @@ impl fmt::Display for Error {
     }
 }
 
-#[cfg(feature = "v3")]
+#[cfg(feature = "v3_openssl")]
 impl From<openssl::error::ErrorStack> for Error {
     fn from(err: openssl::error::ErrorStack) -> Error {
         Error::Crypto(err.to_string())