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Add user secret in mix to encrypt keys with password

This commit is contained in:
Alex 2022-05-23 17:31:53 +02:00
parent 378cbd76d0
commit cb9b64a184
Signed by: lx
GPG Key ID: 0E496D15096376BE
6 changed files with 160 additions and 30 deletions
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2
.gitignore vendored
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@ -1,4 +1,4 @@
/target
.vimrc
test.sh
env.sh
mailrage.toml

22
README.md
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@ -61,19 +61,25 @@ Keys that are stored in K2V under PK `keys`:
- if a password is used, `password:<truncated(128bit) argon2 digest of password using salt S>`:
- a 32-byte salt `Skey`
- followed a secret box
- that is encrypted with a strong argon2 digest of the password (using the salt `Skey`)
- that is encrypted with a strong argon2 digest of the password (using the salt `Skey`) and a user secret (see below)
- that contains the master secret key and the curve25519 private key
User secret: an additionnal secret that is added to the password when deriving the encryption key for the secret box.
This additionnal secret should not be stored in K2V/S3, so that just knowing a user's password isn't enough to be able
to decrypt their mailbox (supposing the attacker has a dump of their K2V/S3 bucket).
This user secret should typically be stored in the LDAP database or just in the configuration file when using
the static login provider.
Operations:
- **Initialize**(`password`):
- **Initialize**(`user_secret`, `password`):
- if `"salt"` or `"public"` already exist, BAIL
- generate salt `S` (32 random bytes)
- generate `public`, `private` (curve25519 keypair)
- generate `master` (secretbox secret key)
- calculate `digest = argon2_S(password)`
- generate salt `Skey` (32 random bytes)
- calculate `key = argon2_Skey(password)`
- calculate `key = argon2_Skey(user_secret + password)`
- serialize `box_contents = (private, master)`
- seal box `blob = seal_key(box_contents)`
- write `S` at `"salt"`
@ -87,12 +93,12 @@ Operations:
- calculate `public` the public key associated with `private`
- write `public` at `"public"`
- **Open**(`password`):
- **Open**(`user_secret`, `password`):
- load `S = read("salt")`
- calculate `digest = argon2_S(password)`
- load `blob = read("password:{hex(digest[..16])}")
- set `Skey = blob[..32]`
- calculate `key = argon2_Skey(password)`
- calculate `key = argon2_Skey(user_secret + password)`
- open secret box `box_contents = open_key(blob[32..])`
- retrieve `master` and `private` from `box_contents`
- retrieve `public = read("public")`
@ -101,18 +107,18 @@ Operations:
- load `public = read("public")`
- check that `public` is the correct public key associated with `private`
- **AddPassword**(`existing_password`, `new_password`):
- **AddPassword**(`user_secret`, `existing_password`, `new_password`):
- load `S = read("salt")`
- calculate `digest = argon2_S(existing_password)`
- load `blob = read("existing_password:{hex(digest[..16])}")
- set `Skey = blob[..32]`
- calculate `key = argon2_Skey(existing_password)`
- calculate `key = argon2_Skey(user_secret + existing_password)`
- open secret box `box_contents = open_key(blob[32..])`
- retrieve `master` and `private` from `box_contents`
- calculate `digest_new = argon2_S(new_password)`
- generate salt `Skeynew` (32 random bytes)
- calculate `key_new = argon2_Skeynew(new_password)`
- calculate `key_new = argon2_Skeynew(user_secret + new_password)`
- serialize `box_contents_new = (private, master)`
- seal box `blob_new = seal_key_new(box_contents_new)`
- write `concat(Skeynew, blob_new)` at `"new_password:{hex(digest_new[..16])}"`

6
src/config.rs
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@ -29,6 +29,10 @@ pub struct LoginStaticUser {
pub aws_secret_access_key: String,
pub bucket: Option<String>,
pub user_secret: String,
#[serde(default)]
pub alternate_user_secrets: Vec<String>,
pub master_key: Option<String>,
pub secret_key: Option<String>,
}
@ -41,6 +45,8 @@ pub struct LoginLdapConfig {
pub username_attr: String,
pub aws_access_key_id_attr: String,
pub aws_secret_access_key_attr: String,
pub user_secret_attr: String,
pub alternate_user_secrets_attr: Option<String>,
pub bucket: Option<String>,
pub bucket_attr: Option<String>,

88
src/login/mod.rs
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@ -16,17 +16,27 @@ use rusoto_signature::Region;
use crate::cryptoblob::*;
/// The trait LoginProvider defines the interface for a login provider that allows
/// to retrieve storage and cryptographic credentials for access to a user account
/// from their username and password.
#[async_trait]
pub trait LoginProvider {
/// The login method takes an account's password as an input to decypher
/// decryption keys and obtain full access to the user's account.
async fn login(&self, username: &str, password: &str) -> Result<Credentials>;
}
/// The struct Credentials represent all of the necessary information to interact
/// with a user account's data after they are logged in.
#[derive(Clone, Debug)]
pub struct Credentials {
/// The storage credentials are used to authenticate access to the underlying storage (S3, K2V)
pub storage: StorageCredentials,
/// The cryptographic keys are used to encrypt and decrypt data stored in S3 and K2V
pub keys: CryptoKeys,
}
/// The struct StorageCredentials contains access key to an S3 and K2V bucket
#[derive(Clone, Debug)]
pub struct StorageCredentials {
pub s3_region: Region,
@ -37,12 +47,28 @@ pub struct StorageCredentials {
pub bucket: String,
}
/// The struct UserSecrets represents intermediary secrets that are mixed in with the user's
/// password when decrypting the cryptographic keys that are stored in their bucket.
/// These secrets should be stored somewhere else (e.g. in the LDAP server or in the
/// local config file), as an additionnal authentification factor so that the password
/// isn't enough just alone to decrypt the content of a user's bucket.
pub struct UserSecrets {
/// The main user secret that will be used to encrypt keys when a new password is added
pub user_secret: String,
/// Alternative user secrets that will be tried when decrypting keys that were encrypted
/// with old passwords
pub alternate_user_secrets: Vec<String>,
}
/// The struct CryptoKeys contains the cryptographic keys used to encrypt and decrypt
/// data in a user's mailbox.
#[derive(Clone, Debug)]
pub struct CryptoKeys {
// Master key for symmetric encryption of mailbox data
/// Master key for symmetric encryption of mailbox data
pub master: Key,
// Public/private keypair for encryption of incomming emails
/// Public/private keypair for encryption of incomming emails (secret part)
pub secret: SecretKey,
/// Public/private keypair for encryption of incomming emails (public part)
pub public: PublicKey,
}
@ -92,7 +118,11 @@ impl StorageCredentials {
}
impl CryptoKeys {
pub async fn init(storage: &StorageCredentials, password: &str) -> Result<Self> {
pub async fn init(
storage: &StorageCredentials,
user_secrets: &UserSecrets,
password: &str,
) -> Result<Self> {
// Check that salt and public don't exist already
let k2v = storage.k2v_client()?;
let (salt_ct, public_ct) = Self::check_uninitialized(&k2v).await?;
@ -118,8 +148,7 @@ impl CryptoKeys {
thread_rng().fill(&mut kdf_salt);
// Calculate key for password secret box
let password_key =
Key::from_slice(&argon2_kdf(&kdf_salt, password.as_bytes(), 32)?).unwrap();
let password_key = user_secrets.derive_password_key(&kdf_salt, password)?;
// Seal a secret box that contains our crypto keys
let password_sealed = seal(&keys.serialize(), &password_key)?;
@ -171,7 +200,11 @@ impl CryptoKeys {
Ok(keys)
}
pub async fn open(storage: &StorageCredentials, password: &str) -> Result<Self> {
pub async fn open(
storage: &StorageCredentials,
user_secrets: &UserSecrets,
password: &str,
) -> Result<Self> {
let k2v = storage.k2v_client()?;
let (ident_salt, expected_public) = Self::load_salt_and_public(&k2v).await?;
@ -199,9 +232,8 @@ impl CryptoKeys {
// Try to open blob
let kdf_salt = &password_blob[..32];
let password_key =
Key::from_slice(&argon2_kdf(kdf_salt, password.as_bytes(), 32)?).unwrap();
let password_openned = open(&password_blob[32..], &password_key)?;
let password_openned =
user_secrets.try_open_encrypted_keys(&kdf_salt, password, &password_blob[32..])?;
let keys = Self::deserialize(&password_openned)?;
if keys.public != expected_public {
@ -235,7 +267,12 @@ impl CryptoKeys {
Ok(keys)
}
pub async fn add_password(&self, storage: &StorageCredentials, password: &str) -> Result<()> {
pub async fn add_password(
&self,
storage: &StorageCredentials,
user_secrets: &UserSecrets,
password: &str,
) -> Result<()> {
let k2v = storage.k2v_client()?;
let (ident_salt, _public) = Self::load_salt_and_public(&k2v).await?;
@ -247,8 +284,7 @@ impl CryptoKeys {
thread_rng().fill(&mut kdf_salt);
// Calculate key for password secret box
let password_key =
Key::from_slice(&argon2_kdf(&kdf_salt, password.as_bytes(), 32)?).unwrap();
let password_key = user_secrets.derive_password_key(&kdf_salt, password)?;
// Seal a secret box that contains our crypto keys
let password_sealed = seal(&self.serialize(), &password_key)?;
@ -453,6 +489,34 @@ impl CryptoKeys {
}
}
impl UserSecrets {
fn derive_password_key_with(user_secret: &str, kdf_salt: &[u8], password: &str) -> Result<Key> {
let tmp = format!("{}\n\n{}", user_secret, password);
Ok(Key::from_slice(&argon2_kdf(&kdf_salt, tmp.as_bytes(), 32)?).unwrap())
}
fn derive_password_key(&self, kdf_salt: &[u8], password: &str) -> Result<Key> {
Self::derive_password_key_with(&self.user_secret, kdf_salt, password)
}
fn try_open_encrypted_keys(
&self,
kdf_salt: &[u8],
password: &str,
encrypted_keys: &[u8],
) -> Result<Vec<u8>> {
let secrets_to_try =
std::iter::once(&self.user_secret).chain(self.alternate_user_secrets.iter());
for user_secret in secrets_to_try {
let password_key = Self::derive_password_key_with(user_secret, kdf_salt, password)?;
if let Ok(res) = open(encrypted_keys, &password_key) {
return Ok(res);
}
}
bail!("Unable to decrypt password blob.");
}
}
// ---- UTIL ----
pub fn argon2_kdf(salt: &[u8], password: &[u8], output_len: usize) -> Result<Vec<u8>> {

6
src/login/static_provider.rs
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@ -60,7 +60,11 @@ impl LoginProvider for StaticLoginProvider {
CryptoKeys::open_without_password(&storage, &master_key, &secret_key).await?
}
(None, None) => {
CryptoKeys::open(&storage, password).await?
let user_secrets = UserSecrets {
user_secret: u.user_secret.clone(),
alternate_user_secrets: u.alternate_user_secrets.clone(),
};
CryptoKeys::open(&storage, &user_secrets, password).await?
}
_ => bail!("Either both master and secret key or none of them must be specified for user"),
};

66
src/main.rs
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@ -38,6 +38,8 @@ enum Command {
FirstLogin {
#[clap(flatten)]
creds: StorageCredsArgs,
#[clap(flatten)]
user_secrets: UserSecretsArgs,
},
/// Initializes key pairs for a user and dumps keys to stdout for usage with static
/// login provider
@ -49,6 +51,8 @@ enum Command {
AddPassword {
#[clap(flatten)]
creds: StorageCredsArgs,
#[clap(flatten)]
user_secrets: UserSecretsArgs,
/// Automatically generate password
#[clap(short, long)]
gen: bool,
@ -57,6 +61,8 @@ enum Command {
DeletePassword {
#[clap(flatten)]
creds: StorageCredsArgs,
#[clap(flatten)]
user_secrets: UserSecretsArgs,
/// Allow to delete all passwords
#[clap(long)]
allow_delete_all: bool,
@ -65,6 +71,8 @@ enum Command {
ShowKeys {
#[clap(flatten)]
creds: StorageCredsArgs,
#[clap(flatten)]
user_secrets: UserSecretsArgs,
},
}
@ -90,6 +98,16 @@ struct StorageCredsArgs {
bucket: String,
}
#[derive(Parser, Debug)]
struct UserSecretsArgs {
/// User secret
#[clap(short = 'U', long, env = "USER_SECRET")]
user_secret: String,
/// Alternate user secrets (comma-separated list of strings)
#[clap(long, env = "ALTERNATE_USER_SECRETS", default_value = "")]
alternate_user_secrets: String,
}
#[tokio::main]
async fn main() -> Result<()> {
if std::env::var("RUST_LOG").is_err() {
@ -106,8 +124,12 @@ async fn main() -> Result<()> {
let server = Server::new(config)?;
server.run().await?;
}
Command::FirstLogin { creds } => {
Command::FirstLogin {
creds,
user_secrets,
} => {
let creds = make_storage_creds(creds);
let user_secrets = make_user_secrets(user_secrets);
println!("Please enter your password for key decryption.");
println!("If you are using LDAP login, this must be your LDAP password.");
@ -118,7 +140,7 @@ async fn main() -> Result<()> {
bail!("Passwords don't match.");
}
CryptoKeys::init(&creds, &password).await?;
CryptoKeys::init(&creds, &user_secrets, &password).await?;
println!("");
println!("Cryptographic key setup is complete.");
@ -153,8 +175,14 @@ async fn main() -> Result<()> {
dump_config(&password, &creds);
dump_keys(&keys);
}
Command::AddPassword { creds, gen } => {
Command::AddPassword {
creds,
user_secrets,
gen,
} => {
let creds = make_storage_creds(creds);
let user_secrets = make_user_secrets(user_secrets);
let existing_password =
rpassword::prompt_password("Enter existing password to decrypt keys: ")?;
let new_password = if gen {
@ -174,19 +202,23 @@ async fn main() -> Result<()> {
password
};
let keys = CryptoKeys::open(&creds, &existing_password).await?;
keys.add_password(&creds, &new_password).await?;
let keys = CryptoKeys::open(&creds, &user_secrets, &existing_password).await?;
keys.add_password(&creds, &user_secrets, &new_password)
.await?;
println!("");
println!("New password added successfully.");
}
Command::DeletePassword {
creds,
user_secrets,
allow_delete_all,
} => {
let creds = make_storage_creds(creds);
let user_secrets = make_user_secrets(user_secrets);
let existing_password = rpassword::prompt_password("Enter password to delete: ")?;
let keys = CryptoKeys::open(&creds, &existing_password).await?;
let keys = CryptoKeys::open(&creds, &user_secrets, &existing_password).await?;
keys.delete_password(&creds, &existing_password, allow_delete_all)
.await?;
@ -198,11 +230,16 @@ async fn main() -> Result<()> {
dump_keys(&keys);
}
}
Command::ShowKeys { creds } => {
Command::ShowKeys {
creds,
user_secrets,
} => {
let creds = make_storage_creds(creds);
let user_secrets = make_user_secrets(user_secrets);
let existing_password = rpassword::prompt_password("Enter key decryption password: ")?;
let keys = CryptoKeys::open(&creds, &existing_password).await?;
let keys = CryptoKeys::open(&creds, &user_secrets, &existing_password).await?;
dump_keys(&keys);
}
}
@ -228,6 +265,19 @@ fn make_storage_creds(c: StorageCredsArgs) -> StorageCredentials {
}
}
fn make_user_secrets(c: UserSecretsArgs) -> UserSecrets {
UserSecrets {
user_secret: c.user_secret,
alternate_user_secrets: c
.alternate_user_secrets
.split(",")
.map(|x| x.trim())
.filter(|x| !x.is_empty())
.map(|x| x.to_string())
.collect(),
}
}
fn dump_config(password: &str, creds: &StorageCredentials) {
println!("[login_static.users.<username>]");
println!(