encryption

lib/ssh-keys/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "ssh-keys"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+aes = "0.8.4"
+bcrypt-pbkdf = "0.10.0"
+ctr = "0.9.2"
+pem = "3.0.4"
+ssh-transport = { path = "../ssh-transport" }

lib/ssh-keys/README.md

@@ -0,0 +1,3 @@
+# ssh-keys
+
+Library for processing OpenSSH keys according to https://github.com/openssh/openssh-portable/blob/a76a6b85108e3032c8175611ecc5746e7131f876/PROTOCOL.key.

lib/ssh-keys/src/crypto.rs

@@ -0,0 +1,97 @@
+use std::str::FromStr;
+
+use aes::cipher::{KeySizeUser, StreamCipher};
+use ssh_transport::parse::{self, Parser};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Cipher {
+    None,
+    Aes256Ctr,
+}
+
+impl FromStr for Cipher {
+    type Err = parse::ParseError;
+
+    fn from_str(ciphername: &str) -> Result<Self, Self::Err> {
+        let cipher = match ciphername {
+            "none" => Cipher::None,
+            "aes256-ctr" => Cipher::Aes256Ctr,
+            _ => {
+                return Err(parse::ParseError(format!(
+                    "unsupported cipher: {ciphername}"
+                )));
+            }
+        };
+        Ok(cipher)
+    }
+}
+
+impl Cipher {
+    pub(crate) fn key_iv_size(&self) -> (usize, usize) {
+        match self {
+            Cipher::None => (0, 0),
+            Cipher::Aes256Ctr => (aes::Aes256::key_size(), 16),
+        }
+    }
+
+    pub(crate) fn decrypt_in_place(&self, data: &mut [u8], key: &[u8], iv: &[u8]) {
+        match self {
+            Cipher::None => unreachable!("cannot decrypt none cipher"),
+            Cipher::Aes256Ctr => {
+                type Aes256Ctr = ctr::Ctr128BE<aes::Aes256>;
+                let mut cipher =
+                    <Aes256Ctr as aes::cipher::KeyIvInit>::new_from_slices(key, iv).unwrap();
+                cipher.apply_keystream(data);
+            }
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Kdf {
+    None,
+    BCrypt { salt: [u8; 16], rounds: u32 },
+}
+impl Kdf {
+    pub(crate) fn from_str_and_options(
+        kdfname: &str,
+        kdfoptions: &[u8],
+    ) -> Result<Self, parse::ParseError> {
+        let kdf = match kdfname {
+            "none" => {
+                if !kdfoptions.is_empty() {
+                    return Err(parse::ParseError(format!(
+                        "KDF options must be empty for none KDF"
+                    )));
+                }
+                Kdf::None
+            }
+            "bcrypt" => {
+                let mut opts = Parser::new(kdfoptions);
+                let salt = opts.string()?;
+                let rounds = opts.u32()?;
+                Kdf::BCrypt {
+                    salt: salt
+                        .try_into()
+                        .map_err(|_| parse::ParseError(format!("incorrect bcrypt salt len")))?,
+                    rounds,
+                }
+            }
+            _ => {
+                return Err(parse::ParseError(format!("unsupported KDF: {kdfname}")));
+            }
+        };
+        Ok(kdf)
+    }
+
+    pub(crate) fn derive(&self, passphrase: &str, output: &mut [u8]) -> parse::Result<()> {
+        match self {
+            Self::None => unreachable!("should not attempt to derive passphrase from none"),
+            Self::BCrypt { salt, rounds } => {
+                bcrypt_pbkdf::bcrypt_pbkdf(passphrase, salt, *rounds, output).map_err(|err| {
+                    parse::ParseError(format!("error when performing key derivation: {err}"))
+                })
+            }
+        }
+    }
+}

lib/ssh-keys/src/lib.rs

@@ -0,0 +1,220 @@
+mod crypto;
+
+use crypto::{Cipher, Kdf};
+use ssh_transport::{
+    key::PublicKey,
+    parse::{self, Parser},
+};
+
+pub struct EncryptedPrivateKeys {
+    pub public_keys: Vec<PublicKey>,
+    pub cipher: Cipher,
+    pub kdf: Kdf,
+    pub encrypted_private_keys: Vec<u8>,
+}
+
+pub struct PlaintextPrivateKey {
+    pub private_key: PrivateKeyType,
+    pub comment: String,
+}
+
+pub enum PrivateKeyType {
+    Ed25519 {
+        public_key: [u8; 32],
+        private_key: [u8; 32],
+    },
+}
+
+const MAGIC: &[u8; 15] = b"openssh-key-v1\0";
+
+impl EncryptedPrivateKeys {
+    /// Parse OpenSSH private keys, either armored or not.
+    pub fn parse_unencrypted(content: &[u8]) -> parse::Result<Self> {
+        // https://github.com/openssh/openssh-portable/blob/a76a6b85108e3032c8175611ecc5746e7131f876/PROTOCOL.key
+        let pem: pem::Pem; // lifetime extension
+        let content = if content.starts_with(b"openssh-key-v1") {
+            content
+        } else if content.starts_with(b"-----BEGIN OPENSSH PRIVATE KEY-----") {
+            pem = pem::parse(content)
+                .map_err(|err| parse::ParseError(format!("invalid PEM format: {err}")))?;
+            pem.contents()
+        } else {
+            return Err(parse::ParseError("invalid SSH key".to_owned()));
+        };
+
+        let mut p = Parser::new(content);
+
+        let magic = p.array::<{ MAGIC.len() }>()?;
+        if magic != *MAGIC {
+            return Err(parse::ParseError(
+                "invalid magic, not an SSH key?".to_owned(),
+            ));
+        }
+
+        let ciphername = p.utf8_string()?;
+        let cipher = ciphername.parse::<Cipher>()?;
+        let kdfname = p.utf8_string()?;
+        let kdfoptions = p.string()?;
+        let kdf = Kdf::from_str_and_options(kdfname, kdfoptions)?;
+        let keynum = p.u32()?;
+
+        let mut public_keys = Vec::new();
+
+        for _ in 0..keynum {
+            let pubkey = p.string()?;
+            let pubkey = PublicKey::from_wire_encoding(pubkey)?;
+            public_keys.push(pubkey);
+        }
+
+        let priv_keys = p.string()?;
+
+        Ok(EncryptedPrivateKeys {
+            public_keys,
+            cipher,
+            kdf,
+            encrypted_private_keys: priv_keys.to_owned(),
+        })
+    }
+
+    pub fn requires_passphrase(&self) -> bool {
+        (!matches!(self.kdf, Kdf::None)) && (!matches!(self.cipher, Cipher::None))
+    }
+
+    pub fn parse_private(
+        &self,
+        passphrase: Option<&str>,
+    ) -> parse::Result<Vec<PlaintextPrivateKey>> {
+        let mut data = self.encrypted_private_keys.clone();
+        if self.requires_passphrase() {
+            let Some(passphrase) = passphrase else {
+                panic!("missing passphrase for encrypted key");
+            };
+            if passphrase.is_empty() {
+                return Err(parse::ParseError(format!("empty passphrase")));
+            }
+
+            let (key_size, iv_size) = self.cipher.key_iv_size();
+
+            let mut output = vec![0; key_size + iv_size];
+            self.kdf.derive(passphrase, &mut output)?;
+            let (key, iv) = output.split_at(key_size);
+            self.cipher.decrypt_in_place(&mut data, &key, &iv);
+        }
+
+        let mut p = Parser::new(&self.encrypted_private_keys);
+        let checkint1 = p.u32()?;
+        let checkint2 = p.u32()?;
+        if checkint1 != checkint2 {
+            return Err(parse::ParseError(format!(
+                "failed sanity check, invalid key or password ({checkint1}!={checkint2})"
+            )));
+        }
+
+        let mut result_keys = Vec::new();
+
+        for pubkey in &self.public_keys {
+            let keytype = match pubkey {
+                PublicKey::Ed25519 { public_key } => {
+                    let alg = p.utf8_string()?;
+                    if alg != "ssh-ed25519" {
+                        return Err(parse::ParseError(format!(
+                            "algorithm mismatch. pubkey: ssh-ed25519, privkey: {alg}"
+                        )));
+                    }
+                    let enc_a = p.string()?; // ENC(A)
+                    if enc_a != public_key {
+                        return Err(parse::ParseError(format!("public key mismatch")));
+                    }
+                    let k_enc_a = p.string()?; // k || ENC(A)
+                    if k_enc_a.len() != 64 {
+                        return Err(parse::ParseError(format!(
+                            "invalid len for ed25519 keypair: {}, expected 64",
+                            k_enc_a.len()
+                        )));
+                    }
+                    let (k, enc_a) = k_enc_a.split_at(32);
+                    if enc_a != public_key {
+                        // Yes, ed25519 SSH keys seriously store the public key THREE TIMES.
+                        return Err(parse::ParseError(format!("public key mismatch")));
+                    }
+                    let private_key = k.try_into().unwrap();
+                    PrivateKeyType::Ed25519 {
+                        public_key: *public_key,
+                        private_key,
+                    }
+                }
+            };
+
+            let comment = p.utf8_string()?;
+
+            result_keys.push(PlaintextPrivateKey {
+                private_key: keytype,
+                comment: comment.to_owned(),
+            });
+        }
+
+        // verify padding
+        for i in 1_u8..=255 {
+            if p.has_data() {
+                let b = p.u8()?;
+                if b != i {
+                    return Err(parse::ParseError(format!(
+                        "private key padding is incorrect: {b} != {i}"
+                    )));
+                }
+            }
+        }
+
+        Ok(result_keys)
+    }
+}
+
+impl PrivateKeyType {
+    pub fn public_key(&self) -> PublicKey {
+        match *self {
+            Self::Ed25519 { public_key, .. } => PublicKey::Ed25519 { public_key },
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Cipher, EncryptedPrivateKeys, Kdf, PrivateKeyType};
+
+    // ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHPaiIO6MePXM/QCJWVge1k4dsiefPr4taP9VJbCtXdx uwu
+    // Password: 'test'
+    const _TEST_ED25519_AES256_CTR: &[u8] = b"-----BEGIN OPENSSH PRIVATE KEY-----
+b3BlbnNzaC1rZXktdjEAAAAACmFlczI1Ni1jdHIAAAAGYmNyeXB0AAAAGAAAABA5S8LoGs
+SYFE1uIAlgK4I/AAAAGAAAAAEAAAAzAAAAC3NzaC1lZDI1NTE5AAAAIHPaiIO6MePXM/QC
+JWVge1k4dsiefPr4taP9VJbCtXdxAAAAkB9StlI/JgwhtvDGx7v08RAa76W6aXSgbDJTU/
+KNPzv0yXhCRleYltud2W2R3G6lElGKBgLfC6U944U8ZFHQQevQIHeSGPkbLGklTXrrrLl7
+ZdWF8er/J/gA0H1T0QE/NYiHxY4NdBzYc4GKCBItOmIT8K/4bsMmh7VXtO0WmkmhoumnLX
+rsOKyxcDiMs2J8cg==
+-----END OPENSSH PRIVATE KEY-----
+";
+
+    // ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIP60Q8iOyatiPeJbpQ8JVoZazukcSwhnKrg+wzw7/JZQ uwu
+    // no password
+    const TEST_ED25519_NONE: &[u8] = b"-----BEGIN OPENSSH PRIVATE KEY-----
+b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
+QyNTUxOQAAACD+tEPIjsmrYj3iW6UPCVaGWs7pHEsIZyq4PsM8O/yWUAAAAIj6bZmH+m2Z
+hwAAAAtzc2gtZWQyNTUxOQAAACD+tEPIjsmrYj3iW6UPCVaGWs7pHEsIZyq4PsM8O/yWUA
+AAAEAdSh0yeEtOyIa0mzMH36U77BNkiuQkERT8TVTrOOgPyP60Q8iOyatiPeJbpQ8JVoZa
+zukcSwhnKrg+wzw7/JZQAAAAA3V3dQEC
+-----END OPENSSH PRIVATE KEY-----
+";
+
+    #[test]
+    fn unencrypted_ed25519() {
+        let keys = EncryptedPrivateKeys::parse_unencrypted(TEST_ED25519_NONE).unwrap();
+        assert_eq!(keys.public_keys.len(), 1);
+        assert_eq!(keys.cipher, Cipher::None);
+        assert_eq!(keys.kdf, Kdf::None);
+
+        let decrypted = keys.parse_private(None).unwrap();
+        assert_eq!(decrypted.len(), 1);
+        let key = decrypted.first().unwrap();
+        assert_eq!(key.comment, "uwu");
+        assert!(matches!(key.private_key, PrivateKeyType::Ed25519 { .. }));
+    }
+}