Add SRP-6 support

Use the newly introduced C99 FFI API to implement both
server- and client- side functionalities.
Enable SRP-6 support only when botan version >= 3.0 is used
("botan3" cargo feature).

Author: Rostyslav Khudolii

botan-sys/src/lib.rs

@@ -20,6 +20,8 @@ mod rng;
 mod utils;
 mod version;
 mod x509;
+#[cfg(feature="botan3")]
+mod srp6;
 
 pub use block::*;
 pub use cipher::*;
@@ -38,3 +40,5 @@ pub use rng::*;
 pub use utils::*;
 pub use version::*;
 pub use x509::*;
+#[cfg(feature="botan3")]
+pub use srp6::*;

botan-sys/src/srp6.rs

@@ -0,0 +1,54 @@
+#![allow(non_camel_case_types)]
+
+use cty::{c_char, c_int};
+use rng::botan_rng_t;
+
+pub enum botan_srp6_server_session_struct {}
+pub type botan_srp6_server_session_t = *mut botan_srp6_server_session_struct;
+
+extern "C" {
+    pub fn botan_srp6_server_session_init(srp6: *mut botan_srp6_server_session_t) -> c_int;
+    pub fn botan_srp6_server_session_destroy(srp6: botan_srp6_server_session_t) -> c_int;
+    pub fn botan_srp6_server_session_step1(
+        srp6: botan_srp6_server_session_t,
+        v: *const u8,
+        v_len: usize,
+        group_id: *const c_char,
+        hash_id: *const c_char,
+        rng_obj: botan_rng_t,
+        b_pub: *mut u8,
+        b_pub_len: *mut usize
+    ) -> c_int;
+    pub fn botan_srp6_server_session_step2(
+        srp6: botan_srp6_server_session_t,
+        a: *const u8,
+        a_len: usize,
+        key: *mut u8,
+        key_len: *mut usize,
+    ) -> c_int;
+    pub fn botan_generate_srp6_verifier(
+        identifier: *const c_char,
+        password: *const c_char,
+        salt: *const u8,
+        salt_len: usize,
+        group_id: *const c_char,
+        hash_id: *const c_char,
+        verifier: *mut u8,
+        verifier_len: *mut usize
+    ) -> c_int;
+    pub fn botan_srp6_client_agree(
+        username: *const c_char,
+        password: *const c_char,
+        group_id: *const c_char,
+        hash_id: *const c_char,
+        salt: *const u8,
+        salt_len: usize,
+        b: *const u8,
+        b_len: usize,
+        rng_obj: botan_rng_t,
+        a: *mut u8,
+        a_len: *mut usize,
+        key: *mut u8,
+        key_len: *mut usize,
+    ) -> c_int;
+}

botan/src/lib.rs

@@ -117,6 +117,8 @@ mod rng;
 mod utils;
 mod version;
 mod x509;
+#[cfg(feature="botan3")]
+mod srp6;
 
 pub use crate::mp::*;
 pub use crate::rng::*;
@@ -136,3 +138,5 @@ pub use pk_ops::*;
 pub use pubkey::*;
 pub use version::*;
 pub use x509::*;
+#[cfg(feature="botan3")]
+pub use srp6::*;

botan/src/srp6.rs

@@ -0,0 +1,185 @@
+//! SRP-6a (RFC 5054 compatatible)
+//!
+//! This module contains the [`ServerSession`] type and the client side functions.
+//!
+//! # Examples
+//!
+//! ```
+//! use botan::RandomNumberGenerator;
+//! use botan::{ServerSession, generate_srp6_verifier, srp6_client_agree};
+//!
+//! let mut rng = RandomNumberGenerator::new_system().expect("Failed to create a random number generator");
+//! let mut server = ServerSession::new().expect("Failed to create a SRP6 server session");
+//! let salt = rng.read(24).expect("Failed to generate salt");
+//! let verifier = generate_srp6_verifier("alice", "password123", &salt, "modp/srp/1024", "SHA-512").expect("Failed to generate SRP6 verifier");
+//! let b_pub = server.step1(&verifier, "modp/srp/1024", "SHA-512", &rng).expect("Failed to calculate server B value");
+//! let (a_pub, client_key) = srp6_client_agree("alice", "password123", "modp/srp/1024", "SHA-512", &salt, &b_pub, &rng).expect("Failed to generate client key");
+//! let server_key = server.step2(&a_pub).expect("Failed to generate server key");
+//! assert_eq!(client_key, server_key);
+//! ```
+
+use crate::{utils::*, RandomNumberGenerator};
+use botan_sys::*;
+
+/// An SRP-6 server session
+#[derive(Debug)]
+pub struct ServerSession {
+    obj: botan_srp6_server_session_t,
+}
+
+botan_impl_drop!(ServerSession, botan_srp6_server_session_destroy);
+
+impl ServerSession {
+    /// Returns a new server session object.
+    ///
+    /// # Errors
+    ///
+    /// Returns [`ErrorType::OutOfMemory`] if memory is exhausted
+    pub fn new() -> Result<Self> {
+        Ok(Self {
+            obj: botan_init!(botan_srp6_server_session_init)?,
+        })
+    }
+
+    /// Server side step 1. Returns SRP-6 B value.
+    ///
+    /// # Arguments
+    ///
+    /// `verifier`: the verification value saved from client registration
+    /// `group_id`: the SRP group id
+    /// `hash_id`: the SRP hash in use
+    /// `rng`: a random number generator
+    ///
+    /// # Errors
+    ///
+    /// Returns [`ErrorType::BadParameter`] if SRP group/hash id is invalid.
+    pub fn step1(
+        &mut self,
+        verifier: &[u8],
+        group_id: &str,
+        hash_id: &str,
+        rng: &RandomNumberGenerator,
+    ) -> Result<Vec<u8>> {
+        let group_id = make_cstr(group_id)?;
+        let hash_id = make_cstr(hash_id)?;
+        call_botan_ffi_returning_vec_u8(128, &|b_pub, b_pub_len| unsafe {
+            botan_srp6_server_session_step1(
+                self.obj,
+                verifier.as_ptr(),
+                verifier.len(),
+                group_id.as_ptr(),
+                hash_id.as_ptr(),
+                rng.handle(),
+                b_pub,
+                b_pub_len,
+            )
+        })
+    }
+
+    /// Server side step 2. Returns shared symmetric key.
+    ///
+    /// # Arguments
+    ///
+    /// `a_pub`: the client's value
+    ///
+    /// # Errors
+    ///
+    /// Returns [`ErrorType::BadParameter`] if the A value is invalid.
+    pub fn step2(&self, a_pub: &[u8]) -> Result<Vec<u8>> {
+        call_botan_ffi_returning_vec_u8(128, &|key, key_len| unsafe {
+            botan_srp6_server_session_step2(self.obj, a_pub.as_ptr(), a_pub.len(), key, key_len)
+        })
+    }
+}
+
+/// Returns a new SRP-6 verifier.
+///
+/// `identifier`: a username or other client identifier
+/// `password`: the secret used to authenticate user
+/// `salt`: a randomly chosen value, at least 128 bits long
+/// `group_id`: the SRP group id
+/// `hash_id`: the SRP hash in use
+///
+/// # Error
+///
+/// Returns [`ErrorType::BadParameter`] if SRP group/hash id is invalid.
+/// Returns [`ErrorType::BadParameter`] if salt is too short.
+pub fn generate_srp6_verifier(
+    identifier: &str,
+    password: &str,
+    salt: &[u8],
+    group_id: &str,
+    hash_id: &str,
+) -> Result<Vec<u8>> {
+    if salt.len() * 8 < 128 {
+        return Err(Error::with_message(
+            ErrorType::BadParameter,
+            "Salt is too short".to_string(),
+        ));
+    }
+
+    let identifier = make_cstr(identifier)?;
+    let password = make_cstr(password)?;
+    let group_id = make_cstr(group_id)?;
+    let hash_id = make_cstr(hash_id)?;
+
+    call_botan_ffi_returning_vec_u8(128, &|verifier, verifier_len| unsafe {
+        botan_generate_srp6_verifier(
+            identifier.as_ptr(),
+            password.as_ptr(),
+            salt.as_ptr(),
+            salt.len(),
+            group_id.as_ptr(),
+            hash_id.as_ptr(),
+            verifier,
+            verifier_len,
+        )
+    })
+}
+
+/// SRP6a Client side. Returns the client public key and the shared secret key.
+///
+/// `username`: the username we are attempting login for
+/// `password`: the password we are attempting to use
+/// `salt`: the salt value sent by the server
+/// `group_id`: specifies the shared SRP group
+/// `hash_id`: specifies a secure hash function
+/// `b_pub`: is the server's public value
+/// `rng`: rng is a random number generator
+///
+/// # Error
+///
+/// Returns [`ErrorType::BadParameter`] if SRP group/hash id is invalid.
+/// Returns [`ErrorType::BadParameter`] if the B value is invalid.
+pub fn srp6_client_agree(
+    username: &str,
+    password: &str,
+    group_id: &str,
+    hash_id: &str,
+    salt: &[u8],
+    b_pub: &[u8],
+    rng: &RandomNumberGenerator,
+) -> Result<(Vec<u8>, Vec<u8>)> {
+    let username = make_cstr(username)?;
+    let password = make_cstr(password)?;
+    let group_id = make_cstr(group_id)?;
+    let hash_id = make_cstr(hash_id)?;
+
+    call_botan_ffi_returning_vec_u8_pair(128, 128, &|a, a_len, key, key_len| unsafe {
+        botan_srp6_client_agree(
+            username.as_ptr(),
+            password.as_ptr(),
+            group_id.as_ptr(),
+            hash_id.as_ptr(),
+            salt.as_ptr(),
+            salt.len(),
+            b_pub.as_ptr(),
+            b_pub.len(),
+            rng.handle(),
+            a,
+            a_len,
+            key,
+            key_len,
+        )
+    })
+}

botan/src/utils.rs

@@ -49,6 +49,43 @@ pub(crate) fn call_botan_ffi_returning_vec_u8(
     Ok(output)
 }
 
+#[cfg(feature = "botan3")]
+pub(crate) fn call_botan_ffi_returning_vec_u8_pair(
+    mut initial_size1: usize,
+    mut initial_size2: usize,
+    cb: &dyn Fn(*mut u8, *mut usize, *mut u8, *mut usize) -> c_int,
+) -> Result<(Vec<u8>, Vec<u8>)> {
+    let mut out1 = vec![0; initial_size1];
+    let mut out1_len = out1.len();
+    let mut out2 = vec![0; initial_size2];
+    let mut out2_len = out2.len();
+    let rc = cb(
+        out1.as_mut_ptr(),
+        &mut out1_len,
+        out2.as_mut_ptr(),
+        &mut out2_len,
+    );
+    match rc {
+        0 => {
+            assert!(out1_len <= out1.len());
+            assert!(out2_len <= out2.len());
+            out1.resize(out1_len, 0);
+            out2.resize(out2_len, 0);
+            Ok((out1, out2))
+        }
+        BOTAN_FFI_ERROR_INSUFFICIENT_BUFFER_SPACE => {
+            if out1_len > out1.len() {
+                initial_size1 = out1_len;
+            }
+            if out2_len > out2.len() {
+                initial_size2 = out2_len;
+            }
+            call_botan_ffi_returning_vec_u8_pair(initial_size1, initial_size2, cb)
+        }
+        _ => Err(Error::from_rc(rc)),
+    }
+}
+
 fn cstr_slice_to_str(raw_cstr: &[u8]) -> Result<String> {
     let cstr = CStr::from_bytes_with_nul(raw_cstr).map_err(Error::conversion_error)?;
     Ok(cstr.to_str().map_err(Error::conversion_error)?.to_owned())

botan/tests/tests.rs

@@ -913,3 +913,62 @@ fn test_totp() -> Result<(), botan::Error> {
     assert!(!totp.check(90693936, 59 + 31, 1)?);
     Ok(())
 }
+
+#[cfg(feature = "botan3")]
+#[test]
+fn test_srp6() -> Result<(), botan::Error> {
+    const IDENTITY: &str = "alice";
+    const PASSWORD: &str = "password123";
+    let mut rng = botan::RandomNumberGenerator::new_system()?;
+
+    // Test successful authentication
+    let mut server = botan::ServerSession::new()?;
+    let salt = rng.read(24)?;
+    let verifier =
+        botan::generate_srp6_verifier(IDENTITY, PASSWORD, &salt, "modp/srp/1024", "SHA-512")?;
+    let b_pub = server.step1(&verifier, "modp/srp/1024", "SHA-512", &rng)?;
+    let (a_pub, client_key) = botan::srp6_client_agree(
+        IDENTITY,
+        PASSWORD,
+        "modp/srp/1024",
+        "SHA-512",
+        &salt,
+        &b_pub,
+        &rng,
+    )?;
+    let server_key = server.step2(&a_pub)?;
+    assert_eq!(client_key, server_key);
+
+    // Test wrong server's B value
+    let salt = rng.read(24)?;
+    let b = b"BD0C6151 2C692C0C B6D041FA 01BB152D 4916A1E7 7AF46AE1 05393011 \
+    BAF38964 DC46A067 0DD125B9 5A981652 236F99D9 B681CBF8 7837EC99 \
+    6C6DA044 53728610 D0C6DDB5 8B318885 D7D82C7F 8DEB75CE 7BD4FBAA \
+    37089E6F 9C6059F3 88838E7A 00030B33 1EB76840 910440B1 B27AAEAE \
+    EB4012B7 D7665238 A8E3FB00 4B117B58";
+    let result = botan::srp6_client_agree(
+        IDENTITY,
+        PASSWORD,
+        "modp/srp/1024",
+        "SHA-512",
+        &salt,
+        b,
+        &rng,
+    );
+    assert!(result.is_err());
+
+    // Test wrong client's A value
+    let salt = rng.read(24)?;
+    let verifier =
+        botan::generate_srp6_verifier(IDENTITY, PASSWORD, &salt, "modp/srp/1024", "SHA-512")?;
+    let _ = server.step1(&verifier, "modp/srp/1024", "SHA-512", &rng)?;
+    let a_pub = b"61D5E490 F6F1B795 47B0704C 436F523D D0E560F0 C64115BB 72557EC4 \
+    4352E890 3211C046 92272D8B 2D1A5358 A2CF1B6E 0BFCF99F 921530EC \
+    8E393561 79EAE45E 42BA92AE ACED8251 71E1E8B9 AF6D9C03 E1327F44 \
+    BE087EF0 6530E69F 66615261 EEF54073 CA11CF58 58F0EDFD FE15EFEA \
+    B349EF5D 76988A36 72FAC47B 0769447B";
+    let result = server.step2(a_pub);
+    assert!(result.is_err());
+
+    Ok(())
+}