[pbs-devel] [PATCH proxmox-backup 02/13] key: add fingerprint to key config

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

and set/generate it on
- key creation
- key passphrase change
- key decryption if not already set
- key encryption with master key

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---

Notes:
    v2: simplify after switchover to Fingerprint struct, incorporate
    feedback
    
    an existing passwordless key can be 'updated' non-interactively with
    
    proxmox-backup-client key change-passphrase $path --kdf none
    
    something like this could go into the/some postinst to retro-actively give all
    the PVE generated storage keys a fingerprint field. this only affects the 'key
    show' subcommand (introduced later in this series) or manual checks of the key
    file, any operations actually using the key have access to its CryptConfig and
    thus the fingerprint() function anyway..
    
    an existing passwordless key can be 'updated' non-interactively with
    
    proxmox-backup-client key change-passphrase $path --kdf none
    
    something like this could go into the/some postinst to retro-actively give all
    the PVE generated storage keys a fingerprint field. this only affects the 'key
    show' subcommand (introduced later in this series) or manual checks of the key
    file, any operations actually using the key have access to its CryptConfig and
    thus the fingerprint() function anyway..

 src/backup/crypt_config.rs                 | 16 ++++++++--
 src/backup/key_derivation.rs               | 22 +++++++++++---
 src/bin/proxmox-backup-client.rs           |  6 ++--
 src/bin/proxmox_backup_client/benchmark.rs |  2 +-
 src/bin/proxmox_backup_client/catalog.rs   |  4 +--
 src/bin/proxmox_backup_client/key.rs       | 19 +++++++++---
 src/bin/proxmox_backup_client/mount.rs     |  2 +-
 src/tools/format.rs                        | 34 ++++++++++++++++++++++
 8 files changed, 88 insertions(+), 17 deletions(-)

diff --git a/src/backup/crypt_config.rs b/src/backup/crypt_config.rs
index 8a4fe0e3..7d27706a 100644
--- a/src/backup/crypt_config.rs
+++ b/src/backup/crypt_config.rs
@@ -17,6 +17,8 @@ use openssl::pkcs5::pbkdf2_hmac;
 use openssl::symm::{decrypt_aead, Cipher, Crypter, Mode};
 use serde::{Deserialize, Serialize};
 
+use crate::tools::format::{as_fingerprint, bytes_as_fingerprint};
+
 use proxmox::api::api;
 
 // openssl::sha::sha256(b"Proxmox Backup Encryption Key Fingerprint")
@@ -37,14 +39,18 @@ pub enum CryptMode {
     SignOnly,
 }
 
+#[derive(Debug, Eq, PartialEq, Deserialize, Serialize)]
+#[serde(transparent)]
 /// 32-byte fingerprint, usually calculated with SHA256.
 pub struct Fingerprint {
+    #[serde(with = "bytes_as_fingerprint")]
     bytes: [u8; 32],
 }
 
+/// Display as short key ID
 impl Display for Fingerprint {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{:?}", self.bytes)
+        write!(f, "{}", as_fingerprint(&self.bytes[0..8]))
     }
 }
 
@@ -243,7 +249,13 @@ impl CryptConfig {
     ) -> Result<Vec<u8>, Error> {
 
         let modified = proxmox::tools::time::epoch_i64();
-        let key_config = super::KeyConfig { kdf: None, created, modified, data: self.enc_key.to_vec() };
+        let key_config = super::KeyConfig {
+            kdf: None,
+            created,
+            modified,
+            data: self.enc_key.to_vec(),
+            fingerprint: Some(self.fingerprint()),
+        };
         let data = serde_json::to_string(&key_config)?.as_bytes().to_vec();
 
         let mut buffer = vec![0u8; rsa.size() as usize];
diff --git a/src/backup/key_derivation.rs b/src/backup/key_derivation.rs
index 2c807723..e7b266ab 100644
--- a/src/backup/key_derivation.rs
+++ b/src/backup/key_derivation.rs
@@ -2,6 +2,8 @@ use anyhow::{bail, format_err, Context, Error};
 
 use serde::{Deserialize, Serialize};
 
+use crate::backup::{CryptConfig, Fingerprint};
+
 use proxmox::tools::fs::{file_get_contents, replace_file, CreateOptions};
 use proxmox::try_block;
 
@@ -66,6 +68,9 @@ pub struct KeyConfig {
     pub modified: i64,
     #[serde(with = "proxmox::tools::serde::bytes_as_base64")]
     pub data: Vec<u8>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(default)]
+    pub fingerprint: Option<Fingerprint>,
  }
 
 pub fn store_key_config(
@@ -142,13 +147,14 @@ pub fn encrypt_key_with_passphrase(
         created,
         modified: created,
         data: enc_data,
+        fingerprint: None,
     })
 }
 
 pub fn load_and_decrypt_key(
     path: &std::path::Path,
     passphrase: &dyn Fn() -> Result<Vec<u8>, Error>,
-) -> Result<([u8;32], i64), Error> {
+) -> Result<([u8;32], i64, Fingerprint), Error> {
     do_load_and_decrypt_key(path, passphrase)
         .with_context(|| format!("failed to load decryption key from {:?}", path))
 }
@@ -156,14 +162,14 @@ pub fn load_and_decrypt_key(
 fn do_load_and_decrypt_key(
     path: &std::path::Path,
     passphrase: &dyn Fn() -> Result<Vec<u8>, Error>,
-) -> Result<([u8;32], i64), Error> {
+) -> Result<([u8;32], i64, Fingerprint), Error> {
     decrypt_key(&file_get_contents(&path)?, passphrase)
 }
 
 pub fn decrypt_key(
     mut keydata: &[u8],
     passphrase: &dyn Fn() -> Result<Vec<u8>, Error>,
-) -> Result<([u8;32], i64), Error> {
+) -> Result<([u8;32], i64, Fingerprint), Error> {
     let key_config: KeyConfig = serde_json::from_reader(&mut keydata)?;
 
     let raw_data = key_config.data;
@@ -203,5 +209,13 @@ pub fn decrypt_key(
     let mut result = [0u8; 32];
     result.copy_from_slice(&key);
 
-    Ok((result, created))
+    let fingerprint = match key_config.fingerprint {
+        Some(fingerprint) => fingerprint,
+        None => {
+            let crypt_config = CryptConfig::new(result.clone())?;
+            crypt_config.fingerprint()
+        },
+    };
+
+    Ok((result, created, fingerprint))
 }
diff --git a/src/bin/proxmox-backup-client.rs b/src/bin/proxmox-backup-client.rs
index 70aba77f..c63c7eb6 100644
--- a/src/bin/proxmox-backup-client.rs
+++ b/src/bin/proxmox-backup-client.rs
@@ -1069,7 +1069,7 @@ async fn create_backup(
     let (crypt_config, rsa_encrypted_key) = match keydata {
         None => (None, None),
         Some(key) => {
-            let (key, created) = decrypt_key(&key, &key::get_encryption_key_password)?;
+            let (key, created, _fingerprint) = decrypt_key(&key, &key::get_encryption_key_password)?;
 
             let crypt_config = CryptConfig::new(key)?;
 
@@ -1380,7 +1380,7 @@ async fn restore(param: Value) -> Result<Value, Error> {
     let crypt_config = match keydata {
         None => None,
         Some(key) => {
-            let (key, _) = decrypt_key(&key, &key::get_encryption_key_password)?;
+            let (key, _, _) = decrypt_key(&key, &key::get_encryption_key_password)?;
             Some(Arc::new(CryptConfig::new(key)?))
         }
     };
@@ -1538,7 +1538,7 @@ async fn upload_log(param: Value) -> Result<Value, Error> {
     let crypt_config = match keydata {
         None => None,
         Some(key) => {
-            let (key, _created) = decrypt_key(&key, &key::get_encryption_key_password)?;
+            let (key, _created, _) = decrypt_key(&key, &key::get_encryption_key_password)?;
             let crypt_config = CryptConfig::new(key)?;
             Some(Arc::new(crypt_config))
         }
diff --git a/src/bin/proxmox_backup_client/benchmark.rs b/src/bin/proxmox_backup_client/benchmark.rs
index b0d769e8..e53e43ce 100644
--- a/src/bin/proxmox_backup_client/benchmark.rs
+++ b/src/bin/proxmox_backup_client/benchmark.rs
@@ -151,7 +151,7 @@ pub async fn benchmark(
     let crypt_config = match keyfile {
         None => None,
         Some(path) => {
-            let (key, _) = load_and_decrypt_key(&path, &crate::key::get_encryption_key_password)?;
+            let (key, _, _) = load_and_decrypt_key(&path, &crate::key::get_encryption_key_password)?;
             let crypt_config = CryptConfig::new(key)?;
             Some(Arc::new(crypt_config))
         }
diff --git a/src/bin/proxmox_backup_client/catalog.rs b/src/bin/proxmox_backup_client/catalog.rs
index e4931e10..37ad842f 100644
--- a/src/bin/proxmox_backup_client/catalog.rs
+++ b/src/bin/proxmox_backup_client/catalog.rs
@@ -73,7 +73,7 @@ async fn dump_catalog(param: Value) -> Result<Value, Error> {
     let crypt_config = match keydata {
         None => None,
         Some(key) => {
-            let (key, _created) = decrypt_key(&key, &get_encryption_key_password)?;
+            let (key, _created, _fingerprint) = decrypt_key(&key, &get_encryption_key_password)?;
             let crypt_config = CryptConfig::new(key)?;
             Some(Arc::new(crypt_config))
         }
@@ -170,7 +170,7 @@ async fn catalog_shell(param: Value) -> Result<(), Error> {
     let crypt_config = match keydata {
         None => None,
         Some(key) => {
-            let (key, _created) = decrypt_key(&key, &get_encryption_key_password)?;
+            let (key, _created, _fingerprint) = decrypt_key(&key, &get_encryption_key_password)?;
             let crypt_config = CryptConfig::new(key)?;
             Some(Arc::new(crypt_config))
         }
diff --git a/src/bin/proxmox_backup_client/key.rs b/src/bin/proxmox_backup_client/key.rs
index 8b802b3e..193367e3 100644
--- a/src/bin/proxmox_backup_client/key.rs
+++ b/src/bin/proxmox_backup_client/key.rs
@@ -11,7 +11,11 @@ use proxmox::sys::linux::tty;
 use proxmox::tools::fs::{file_get_contents, replace_file, CreateOptions};
 
 use proxmox_backup::backup::{
-    encrypt_key_with_passphrase, load_and_decrypt_key, store_key_config, KeyConfig,
+    encrypt_key_with_passphrase,
+    load_and_decrypt_key,
+    store_key_config,
+    CryptConfig,
+    KeyConfig,
 };
 use proxmox_backup::tools;
 
@@ -120,7 +124,10 @@ fn create(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error> {
 
     let kdf = kdf.unwrap_or_default();
 
-    let key = proxmox::sys::linux::random_data(32)?;
+    let mut key_array = [0u8; 32];
+    proxmox::sys::linux::fill_with_random_data(&mut key_array)?;
+    let crypt_config = CryptConfig::new(key_array.clone())?;
+    let key = key_array.to_vec();
 
     match kdf {
         Kdf::None => {
@@ -134,6 +141,7 @@ fn create(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error> {
                     created,
                     modified: created,
                     data: key,
+                    fingerprint: Some(crypt_config.fingerprint()),
                 },
             )?;
         }
@@ -145,7 +153,8 @@ fn create(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error> {
 
             let password = tty::read_and_verify_password("Encryption Key Password: ")?;
 
-            let key_config = encrypt_key_with_passphrase(&key, &password)?;
+            let mut key_config = encrypt_key_with_passphrase(&key, &password)?;
+            key_config.fingerprint = Some(crypt_config.fingerprint());
 
             store_key_config(&path, false, key_config)?;
         }
@@ -188,7 +197,7 @@ fn change_passphrase(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error
         bail!("unable to change passphrase - no tty");
     }
 
-    let (key, created) = load_and_decrypt_key(&path, &get_encryption_key_password)?;
+    let (key, created, fingerprint) = load_and_decrypt_key(&path, &get_encryption_key_password)?;
 
     match kdf {
         Kdf::None => {
@@ -202,6 +211,7 @@ fn change_passphrase(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error
                     created, // keep original value
                     modified,
                     data: key.to_vec(),
+                    fingerprint: Some(fingerprint),
                 },
             )?;
         }
@@ -210,6 +220,7 @@ fn change_passphrase(kdf: Option<Kdf>, path: Option<String>) -> Result<(), Error
 
             let mut new_key_config = encrypt_key_with_passphrase(&key, &password)?;
             new_key_config.created = created; // keep original value
+            new_key_config.fingerprint = Some(fingerprint);
 
             store_key_config(&path, true, new_key_config)?;
         }
diff --git a/src/bin/proxmox_backup_client/mount.rs b/src/bin/proxmox_backup_client/mount.rs
index 415fbf9d..6283961e 100644
--- a/src/bin/proxmox_backup_client/mount.rs
+++ b/src/bin/proxmox_backup_client/mount.rs
@@ -182,7 +182,7 @@ async fn mount_do(param: Value, pipe: Option<RawFd>) -> Result<Value, Error> {
     let crypt_config = match keyfile {
         None => None,
         Some(path) => {
-            let (key, _) = load_and_decrypt_key(&path, &crate::key::get_encryption_key_password)?;
+            let (key, _, _) = load_and_decrypt_key(&path, &crate::key::get_encryption_key_password)?;
             Some(Arc::new(CryptConfig::new(key)?))
         }
     };
diff --git a/src/tools/format.rs b/src/tools/format.rs
index 8fe6aa82..c9f50053 100644
--- a/src/tools/format.rs
+++ b/src/tools/format.rs
@@ -102,6 +102,40 @@ impl From<u64> for HumanByte {
     }
 }
 
+pub fn as_fingerprint(bytes: &[u8]) -> String {
+    proxmox::tools::digest_to_hex(bytes)
+        .as_bytes()
+        .chunks(2)
+        .map(|v| std::str::from_utf8(v).unwrap())
+        .collect::<Vec<&str>>().join(":")
+}
+
+pub mod bytes_as_fingerprint {
+    use serde::{Deserialize, Serializer, Deserializer};
+
+    pub fn serialize<S>(
+        bytes: &[u8; 32],
+        serializer: S,
+    ) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let s = crate::tools::format::as_fingerprint(bytes);
+        serializer.serialize_str(&s)
+    }
+
+    pub fn deserialize<'de, D>(
+        deserializer: D,
+    ) -> Result<[u8; 32], D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let mut s = String::deserialize(deserializer)?;
+        s.retain(|c| c != ':');
+        proxmox::tools::hex_to_digest(&s).map_err(serde::de::Error::custom)
+    }
+}
+
 #[test]
 fn correct_byte_convert() {
     fn convert(b: usize) -> String {
-- 
2.20.1