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Scaffold EAP Message Authenticator with HMACMD5
Implement a new type using the hmac and md-5 crates, namespacing md-5 as hmac_md5 to avoid collision with existing crate. Stub out MessageAuthenticator struct & implementation to create HMACMD5 signature buffers from Packet's encode() byte vector. Implement Message-Authenticator input structure for starting the chain of HMAC exchanges and verifying Access-Request messages. Testing: Implemented test to verify Access-Request message HMACMD5 - pass
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RageLtMan
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Aug 4, 2022
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,155 @@ | ||
| use std::fmt; | ||
| use hmac::{Hmac, Mac}; | ||
| use hmac_md5::Md5; | ||
| use crate::core::packet::Packet; | ||
| use crate::core::rfc2869; | ||
|
|
||
| type HmacMd5 = Hmac<Md5>; | ||
|
|
||
| ///! | ||
| // A RADIUS client receiving an Access-Accept, Access-Reject or | ||
| // Access-Challenge with a Message-Authenticator attribute present | ||
| // MUST calculate the correct value of the Message-Authenticator and | ||
| // silently discard the packet if it does not match the value sent. | ||
| // This attribute is not required in Access-Requests which include | ||
| // the User-Password attribute, but is useful for preventing attacks | ||
| // on other types of authentication. This attribute is intended to | ||
| // thwart attempts by an attacker to setup a "rogue" NAS, and perform | ||
| // online dictionary attacks against the RADIUS server. It does not | ||
| // afford protection against "offline" attacks where the attacker | ||
| // intercepts packets containing (for example) CHAP challenge and | ||
| // response, and performs a dictionary attack against those packets | ||
| // offline. | ||
| // A summary of the Message-Authenticator attribute format is shown | ||
| // below. The fields are transmitted from left to right. | ||
| // 0 1 2 | ||
| // 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 | ||
| // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ||
| // | Type | Length | String... | ||
| // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ||
| // Type | ||
| // 80 for Message-Authenticator | ||
| // Length | ||
| // 18 | ||
| // String | ||
| // When present in an Access-Request packet, Message-Authenticator is | ||
| // an HMAC-MD5 [RFC2104] hash of the entire Access-Request packet, | ||
| // including Type, ID, Length and Authenticator, using the shared | ||
| // secret as the key, as follows. | ||
| // Message-Authenticator = HMAC-MD5 (Type, Identifier, Length, | ||
| // Request Authenticator, Attributes) | ||
| // When the message integrity check is calculated the signature | ||
| // string should be considered to be sixteen octets of zero. | ||
| // For Access-Challenge, Access-Accept, and Access-Reject packets, | ||
| // the Message-Authenticator is calculated as follows, using the | ||
| // Request-Authenticator from the Access-Request this packet is in | ||
| // reply to: | ||
| // Message-Authenticator = HMAC-MD5 (Type, Identifier, Length, | ||
| // Request Authenticator, Attributes) | ||
| // When the message integrity check is calculated the signature | ||
| // string should be considered to be sixteen octets of zero. The | ||
| // shared secret is used as the key for the HMAC-MD5 message | ||
| // integrity check. The Message-Authenticator is calculated and | ||
| // inserted in the packet before the Response Authenticator is | ||
| // calculated. | ||
| ///! | ||
| #[derive(Debug, Copy, Clone, PartialEq)] | ||
| pub struct MessageAuthenticator { | ||
| pub value: [u8; 16] | ||
| } | ||
|
|
||
| impl MessageAuthenticator { | ||
|
|
||
| /// Create a new Message-Authenticator from a 16-byte slice | ||
| pub fn from_bytes(bytes: &[u8]) -> Self { | ||
| assert_eq!(bytes.len(), 16); | ||
| let mut arr = [0u8; 16]; | ||
| for (place, element) in arr.iter_mut().zip(bytes.iter()) { | ||
| *place = *element; | ||
| } | ||
| MessageAuthenticator { value: arr } | ||
| } | ||
| /// Create a new Message-Authenticator with zeroed-values | ||
| pub fn new() -> Self { | ||
| MessageAuthenticator { value: [0u8; 16] } | ||
| } | ||
| /// Create a new Message-Authenticator from input packet | ||
| pub fn from_packet(sb: &Packet) -> Self { | ||
| let mut mac = HmacMd5::new_from_slice(sb.get_secret()).unwrap(); | ||
| mac.update(&sb.encode().expect("Failed to encode packet for hmac-md5")[..]); | ||
| Self::from_bytes(&mac.finalize().into_bytes()[..]) | ||
| } | ||
| /// Create a new Message-Authenticator for an Access-Request RADIUS message. | ||
| /// Since this message type is the start of the HMAC-chain, it hashes itself with | ||
| /// the hash-input RADIUS message having a Message-Authenticator equivalent to the | ||
| /// new() method for this code (all zeroes). | ||
| pub fn from_access_request(pkt: &Packet) -> Self { | ||
| Self::from_packet( | ||
| // zero the existing Message-Authenticator | ||
| &Self::new().authenticate_packet(&pkt).unwrap() | ||
| ) | ||
| } | ||
| /// Attempt to create new Packet with signature buffer from this MessageAuthenticator's | ||
| /// value field. | ||
| pub fn authenticate_packet(&self, pkt: &Packet) -> Result<Packet, std::io::Error> { | ||
| let mut req_bytes = pkt.encode().unwrap(); | ||
| let secret = pkt.get_secret(); | ||
| let req_ma_bytes = rfc2869::lookup_message_authenticator(&pkt).unwrap(); | ||
| Self::replace_slice(&mut req_bytes, &req_ma_bytes, &self.value[..]); | ||
| let res = Packet::decode(&req_bytes, secret).unwrap(); | ||
| Ok(res) | ||
| } | ||
| // From https://stackoverflow.com/questions/54150353/how-to-find-and-replace-every-matching-slice-of-bytes-with-another-slice | ||
| fn replace_slice<T>(buf: &mut [T], from: &[T], to: &[T]) | ||
| where | ||
| T: Clone + PartialEq, | ||
| { | ||
| for i in 0..=buf.len() - from.len() { | ||
| if buf[i..].starts_with(from) { | ||
| buf[i..(i + from.len())].clone_from_slice(to); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl fmt::Display for MessageAuthenticator { | ||
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| write!(f, "{:02X?}", self.value) | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use hex; | ||
| use crate::core::packet::Packet; | ||
| use crate::core::message_authenticator::MessageAuthenticator; | ||
| use crate::core::rfc2869; | ||
|
|
||
| #[test] | ||
| fn it_should_authenticate_access_request() -> Result<(), ()> { | ||
| let msg_bytes = hex::decode("01160049b3a5cd2de262bcdbb589752a212e0b2f01067465737404067f00010105060000000150121ca1999b24d5224ddeca96fd7dabac270706000000014f0b023100090174657374").unwrap(); | ||
| let secret = b"somesecretval"; | ||
| let req_packet = Packet::decode(&msg_bytes, &secret[..]).unwrap(); | ||
| assert_eq!(req_packet.encode().unwrap(), msg_bytes); | ||
| let ma_bytes = rfc2869::lookup_message_authenticator(&req_packet).unwrap(); | ||
| let ma = MessageAuthenticator::from_bytes(&ma_bytes); | ||
| let ema = MessageAuthenticator::from_access_request(&req_packet); | ||
|
|
||
| assert_eq!(ma, ema); | ||
| Ok(()) | ||
| } | ||
| #[test] | ||
| fn it_should_authenticate_other_access_request() -> Result<(), ()> { | ||
| let msg_bytes = hex::decode("013200497d39e88ba3783fc183b54d486c629e8501067465737404067f000101050600000001501208c9801fb78909a8b24ad4dc261b2d470706000000014f0b020200090174657374").unwrap(); | ||
| let secret = b"somesecretval"; | ||
| let req_packet = Packet::decode(&msg_bytes, &secret[..]).unwrap(); | ||
| assert_eq!(req_packet.encode().unwrap(), msg_bytes); | ||
| let ma_bytes = rfc2869::lookup_message_authenticator(&req_packet).unwrap(); | ||
| let ma = MessageAuthenticator::from_bytes(&ma_bytes); | ||
| let ema = MessageAuthenticator::from_access_request(&req_packet); | ||
|
|
||
| assert_eq!(ma, ema); | ||
| Ok(()) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -31,3 +31,4 @@ pub mod rfc7055; | |
| pub mod rfc7155; | ||
| pub mod tag; | ||
| pub mod eap; | ||
| pub mod message_authenticator; | ||