feat: replace private cas envelope

Cargo.lock

@@ -751,6 +751,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "78c8292055d1c1df0cce5d180393dc8cce0abec0a7102adb6c7b1eef6016d60a"
 dependencies = [
  "generic-array",
+ "rand_core 0.6.4",
  "typenum",
 ]
 
@@ -1524,10 +1525,12 @@ dependencies = [
 name = "geth-cas"
 version = "0.1.0"
 dependencies = [
+ "aes-gcm",
  "blake3",
  "geth-codec",
  "geth-types",
  "hex",
+ "rand 0.9.4",
  "serde",
  "tempfile",
  "thiserror 2.0.18",

Cargo.toml

@@ -35,6 +35,7 @@ repository = "https://example.invalid/local/geth"
 rust-version = "1.91"
 
 [workspace.dependencies]
+aes-gcm = "0.10"
 anyhow = "1"
 async-trait = "0.1"
 automerge = "0.7"

README.md

@@ -176,8 +176,9 @@ The bootstrap implementation provides:
   `--bearer-secret <secret>`
 - private CAS envelope commands:
   `geth cas add-private <resource> <path>` and
-  `geth cas get-private <resource> <hash> --out <path>`. These use local
-  resource secret epochs and are a prototype envelope, not audited AEAD.
+  `geth cas get-private <resource> <hash> --out <path>`. New writes use an
+  AES-256-GCM envelope bound to the resource and local secret epoch. This does
+  not claim forward secrecy or post-compromise security.
 - local CAS tree objects describe file trees and are stored as CAS blobs
 - local file-root commands: `geth cas root add/list/scan/sync/apply`; root sync
   pulls authorized remote tree metadata and CAS tree bytes into a peer-qualified

crates/geth-cas/Cargo.toml

@@ -6,8 +6,10 @@ rust-version.workspace = true
 license.workspace = true
 
 [dependencies]
+aes-gcm.workspace = true
 blake3.workspace = true
 hex.workspace = true
+rand.workspace = true
 serde.workspace = true
 thiserror.workspace = true
 geth-codec = { path = "../geth-codec" }

crates/geth-cas/src/lib.rs

@@ -4,7 +4,9 @@ use std::collections::{BTreeMap, BTreeSet};
 use std::path::{Path, PathBuf};
 
 pub const CAS_TREE_OBJECT_VERSION: u16 = 1;
-pub const ENCRYPTED_BLOB_ENVELOPE_VERSION: u16 = 1;
+pub const ENCRYPTED_BLOB_ENVELOPE_VERSION: u16 = 2;
+pub const PRIVATE_BLOB_AEAD_ALGORITHM: &str = "geth.aes-256-gcm.v1";
+pub const PRIVATE_BLOB_PROTOTYPE_ALGORITHM: &str = "geth.blake3-xor.v0.prototype";
 
 #[derive(Debug, thiserror::Error)]
 pub enum CasError {
@@ -191,23 +193,50 @@ pub fn encrypt_private_blob(
     resource: &str,
     secret_id: &str,
     epoch: u64,
-    nonce_hex: &str,
     plaintext: &[u8],
 ) -> Result<Vec<u8>, CasError> {
+    let nonce: [u8; 12] = rand::random();
+    encrypt_private_blob_with_nonce(resource, secret_id, epoch, nonce, plaintext)
+}
+
+fn encrypt_private_blob_with_nonce(
+    resource: &str,
+    secret_id: &str,
+    epoch: u64,
+    nonce: [u8; 12],
+    plaintext: &[u8],
+) -> Result<Vec<u8>, CasError> {
+    use aes_gcm::{
+        Aes256Gcm, Nonce,
+        aead::{Aead, KeyInit, Payload},
+    };
+
     let key = private_blob_key(resource, secret_id, epoch);
-    let nonce = decode_32_byte_hex(nonce_hex)?;
-    let ciphertext = xor_keystream(&key, &nonce, plaintext);
-    let tag_hex = private_blob_tag(&key, &nonce, &ciphertext);
+    let cipher = Aes256Gcm::new_from_slice(&key)
+        .map_err(|error| CasError::EncryptedEnvelope(error.to_string()))?;
+    let plaintext_hash = hash_bytes(plaintext);
+    let aad = private_blob_aad(resource, epoch, &plaintext_hash);
+    let ciphertext = cipher
+        .encrypt(
+            Nonce::from_slice(&nonce),
+            Payload {
+                msg: plaintext,
+                aad: aad.as_bytes(),
+            },
+        )
+        .map_err(|_| {
+            CasError::EncryptedEnvelope("private blob AEAD encryption failed".to_owned())
+        })?;
     let envelope = EncryptedBlobEnvelope {
         version: ENCRYPTED_BLOB_ENVELOPE_VERSION,
-        algorithm: "geth.blake3-xor.v0.prototype".to_owned(),
+        algorithm: PRIVATE_BLOB_AEAD_ALGORITHM.to_owned(),
         resource: resource.to_owned(),
         epoch,
-        plaintext_hash: hash_bytes(plaintext),
-        nonce_hex: nonce_hex.to_owned(),
+        plaintext_hash,
+        nonce_hex: hex::encode(nonce),
         ciphertext,
-        tag_hex,
-        note: "prototype private blob envelope; not an audited AEAD and does not claim forward secrecy or post-compromise security".to_owned(),
+        tag_hex: "included-in-aes-gcm-ciphertext".to_owned(),
+        note: "private blob envelope uses AES-256-GCM with a random 96-bit nonce and resource-bound associated data; it does not claim forward secrecy or post-compromise security".to_owned(),
     };
     geth_codec::encode_canonical(&envelope).map_err(CasError::from)
 }
@@ -219,26 +248,53 @@ pub fn decrypt_private_blob(
 ) -> Result<Vec<u8>, CasError> {
     let envelope: EncryptedBlobEnvelope = geth_codec::decode_canonical(envelope_bytes)?;
     if envelope.version != ENCRYPTED_BLOB_ENVELOPE_VERSION {
+        if envelope.version == 1 || envelope.algorithm == PRIVATE_BLOB_PROTOTYPE_ALGORITHM {
+            return Err(CasError::EncryptedEnvelope(
+                "prototype private blob envelopes are no longer accepted; recreate the private blob with this pre-release".to_owned(),
+            ));
+        }
         return Err(CasError::EncryptedEnvelope(format!(
             "unsupported envelope version {}",
             envelope.version
         )));
     }
+    if envelope.algorithm != PRIVATE_BLOB_AEAD_ALGORITHM {
+        return Err(CasError::EncryptedEnvelope(format!(
+            "unsupported encrypted blob algorithm {}",
+            envelope.algorithm
+        )));
+    }
     if envelope.resource != resource {
         return Err(CasError::EncryptedEnvelope(format!(
             "envelope resource {} does not match requested resource {resource}",
             envelope.resource
         )));
     }
-    let key = private_blob_key(resource, secret_id, envelope.epoch);
-    let nonce = decode_32_byte_hex(&envelope.nonce_hex)?;
-    let expected_tag = private_blob_tag(&key, &nonce, &envelope.ciphertext);
-    if expected_tag != envelope.tag_hex {
+    if envelope.tag_hex != "included-in-aes-gcm-ciphertext" {
         return Err(CasError::EncryptedEnvelope(
-            "encrypted blob tag verification failed".to_owned(),
+            "invalid AES-GCM envelope tag marker".to_owned(),
         ));
     }
-    let plaintext = xor_keystream(&key, &nonce, &envelope.ciphertext);
+    use aes_gcm::{
+        Aes256Gcm, Nonce,
+        aead::{Aead, KeyInit, Payload},
+    };
+    let key = private_blob_key(resource, secret_id, envelope.epoch);
+    let nonce = decode_hex_exact::<12>(&envelope.nonce_hex)?;
+    let cipher = Aes256Gcm::new_from_slice(&key)
+        .map_err(|error| CasError::EncryptedEnvelope(error.to_string()))?;
+    let aad = private_blob_aad(resource, envelope.epoch, &envelope.plaintext_hash);
+    let plaintext = cipher
+        .decrypt(
+            Nonce::from_slice(&nonce),
+            Payload {
+                msg: envelope.ciphertext.as_ref(),
+                aad: aad.as_bytes(),
+            },
+        )
+        .map_err(|_| {
+            CasError::EncryptedEnvelope("private blob AEAD verification failed".to_owned())
+        })?;
     let plaintext_hash = hash_bytes(&plaintext);
     if plaintext_hash != envelope.plaintext_hash {
         return Err(CasError::EncryptedEnvelope(
@@ -249,42 +305,25 @@ pub fn decrypt_private_blob(
 }
 
 fn private_blob_key(resource: &str, secret_id: &str, epoch: u64) -> [u8; 32] {
-    let material = format!("geth.private-blob.v0\0{resource}\0{secret_id}\0{epoch}");
+    let material = format!("geth.private-blob.aes-256-gcm.v1\0{resource}\0{secret_id}\0{epoch}");
     *blake3::hash(material.as_bytes()).as_bytes()
 }
 
-fn xor_keystream(key: &[u8; 32], nonce: &[u8; 32], input: &[u8]) -> Vec<u8> {
-    let mut out = Vec::with_capacity(input.len());
-    for (chunk_index, chunk) in input.chunks(32).enumerate() {
-        let mut block_input = Vec::with_capacity(40);
-        block_input.extend_from_slice(nonce);
-        block_input.extend_from_slice(&(chunk_index as u64).to_le_bytes());
-        let block = blake3::keyed_hash(key, &block_input);
-        out.extend(
-            chunk
-                .iter()
-                .zip(block.as_bytes().iter())
-                .map(|(byte, mask)| byte ^ mask),
-        );
-    }
-    out
+fn private_blob_aad(resource: &str, epoch: u64, plaintext_hash: &BlobHash) -> String {
+    format!(
+        "{}\0{}\0{}\0{}",
+        PRIVATE_BLOB_AEAD_ALGORITHM, resource, epoch, plaintext_hash
+    )
 }
 
-fn private_blob_tag(key: &[u8; 32], nonce: &[u8; 32], ciphertext: &[u8]) -> String {
-    let mut input = Vec::with_capacity(nonce.len() + ciphertext.len());
-    input.extend_from_slice(nonce);
-    input.extend_from_slice(ciphertext);
-    blake3::keyed_hash(key, &input).to_hex().to_string()
+fn decode_hex_exact<const N: usize>(hex: &str) -> Result<[u8; N], CasError> {
+    if hex.len() != N * 2 {
+        return Err(CasError::EncryptedEnvelope(format!(
+            "nonce must be {N} bytes encoded as lowercase hex"
+        )));
     }
-
-fn decode_32_byte_hex(hex: &str) -> Result<[u8; 32], CasError> {
-    if hex.len() != 64 {
-        return Err(CasError::EncryptedEnvelope(
-            "nonce must be 32 bytes encoded as lowercase hex".to_owned(),
-        ));
-    }
-    let mut bytes = [0_u8; 32];
-    for index in 0..32 {
+    let mut bytes = [0_u8; N];
+    for index in 0..N {
         bytes[index] = u8::from_str_radix(&hex[index * 2..index * 2 + 2], 16)
             .map_err(|error| CasError::EncryptedEnvelope(format!("invalid nonce hex: {error}")))?;
     }
@@ -769,11 +808,15 @@ mod tests {
     }
 
     #[test]
-    fn private_blob_envelope_roundtrips_and_checks_resource() {
+    fn private_blob_envelope_uses_aead_and_checks_bound_context() {
         let plaintext = b"private geth bytes";
-        let nonce = "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f";
-        let envelope =
-            encrypt_private_blob("resource:cas:private", "secret:test", 1, nonce, plaintext)
+        let envelope = encrypt_private_blob_with_nonce(
+            "resource:cas:private",
+            "secret:test",
+            1,
+            [7; 12],
+            plaintext,
+        )
         .expect("encrypt");
 
         let decrypted = decrypt_private_blob("resource:cas:private", "secret:test", &envelope)
@@ -781,6 +824,66 @@ mod tests {
         assert_eq!(decrypted, plaintext);
         assert!(decrypt_private_blob("resource:cas:other", "secret:test", &envelope).is_err());
         assert!(decrypt_private_blob("resource:cas:private", "secret:other", &envelope).is_err());
+
+        let decoded: EncryptedBlobEnvelope =
+            geth_codec::decode_canonical(&envelope).expect("decode envelope");
+        assert_eq!(decoded.version, ENCRYPTED_BLOB_ENVELOPE_VERSION);
+        assert_eq!(decoded.algorithm, PRIVATE_BLOB_AEAD_ALGORITHM);
+        assert_eq!(decoded.nonce_hex, "070707070707070707070707");
+        assert_eq!(decoded.tag_hex, "included-in-aes-gcm-ciphertext");
+
+        let mut tampered_ciphertext = decoded.clone();
+        tampered_ciphertext.ciphertext[0] ^= 0x01;
+        let tampered_ciphertext =
+            geth_codec::encode_canonical(&tampered_ciphertext).expect("encode tampered");
+        assert!(
+            decrypt_private_blob("resource:cas:private", "secret:test", &tampered_ciphertext)
+                .is_err()
+        );
+
+        let mut tampered_hash = decoded.clone();
+        tampered_hash.plaintext_hash = hash_bytes(b"other plaintext");
+        let tampered_hash = geth_codec::encode_canonical(&tampered_hash).expect("encode tampered");
+        assert!(
+            decrypt_private_blob("resource:cas:private", "secret:test", &tampered_hash).is_err()
+        );
+    }
+
+    #[test]
+    fn private_blob_envelope_generates_unique_nonces() {
+        let first = encrypt_private_blob("resource:cas:private", "secret:test", 1, b"same")
+            .expect("first encrypt");
+        let second = encrypt_private_blob("resource:cas:private", "secret:test", 1, b"same")
+            .expect("second encrypt");
+        let first: EncryptedBlobEnvelope =
+            geth_codec::decode_canonical(&first).expect("decode first");
+        let second: EncryptedBlobEnvelope =
+            geth_codec::decode_canonical(&second).expect("decode second");
+        assert_ne!(first.nonce_hex, second.nonce_hex);
+        assert_ne!(first.ciphertext, second.ciphertext);
+    }
+
+    #[test]
+    fn prototype_private_blob_envelopes_are_rejected() {
+        let envelope = EncryptedBlobEnvelope {
+            version: 1,
+            algorithm: PRIVATE_BLOB_PROTOTYPE_ALGORITHM.to_owned(),
+            resource: "resource:cas:private".to_owned(),
+            epoch: 1,
+            plaintext_hash: hash_bytes(b"private geth bytes"),
+            nonce_hex: "00".repeat(32),
+            ciphertext: vec![1, 2, 3],
+            tag_hex: "prototype-tag".to_owned(),
+            note: "old prototype".to_owned(),
+        };
+        let encoded = geth_codec::encode_canonical(&envelope).expect("encode prototype");
+        let error = decrypt_private_blob("resource:cas:private", "secret:test", &encoded)
+            .expect_err("reject prototype");
+        assert!(
+            error
+                .to_string()
+                .contains("prototype private blob envelopes")
+        );
     }
 
     #[test]

crates/geth-node/src/lib.rs

@@ -6174,21 +6174,10 @@ pub fn handle_request(
             })?;
             let plaintext = std::fs::read(&path)?;
             let plaintext_hash = geth_cas::hash_bytes(&plaintext);
-            let nonce = geth_crypto::blake3_hex(
-                format!(
-                    "{}\0{}\0{}\0{}",
-                    resource,
-                    secret.secret_id,
-                    secret.epoch,
-                    geth_store::now_ms()
-                )
-                .as_bytes(),
-            );
             let encrypted = geth_cas::encrypt_private_blob(
                 &resource,
                 &secret.secret_id,
                 secret.epoch,
-                &nonce,
                 &plaintext,
             )?;
             let cas = LocalCas::new(node.paths.cas_dir());
@@ -6204,7 +6193,7 @@ pub fn handle_request(
                 plaintext_hash,
                 encrypted_hash: info.hash,
                 size_bytes: info.size_bytes,
-                note: "stored prototype encrypted private blob envelope; no forward secrecy or post-compromise security is claimed".to_owned(),
+                note: "stored AES-256-GCM private blob envelope bound to the resource and secret epoch; no forward secrecy or post-compromise security is claimed".to_owned(),
             })
         }
         ControlRequest::CasGet { hash, out } => {
@@ -6258,7 +6247,9 @@ pub fn handle_request(
                 plaintext_hash: geth_cas::hash_bytes(&plaintext),
                 out,
                 size_bytes: plaintext.len() as u64,
-                note: "decrypted prototype private blob envelope with the latest local resource secret epoch".to_owned(),
+                note:
+                    "decrypted AES-256-GCM private blob envelope with a local resource secret epoch"
+                        .to_owned(),
             })
         }
         ControlRequest::CasHash { path } => Ok(ControlResponse::CasHash {

docs/architecture.md

@@ -478,6 +478,10 @@ The project is structured for future multi-user local-first authorization:
 ## Keyhive/BeeKEM Roadmap
 
 Resource secret epochs are the v0/v1 approximation for private payload access.
+Private CAS writes use an AES-256-GCM envelope keyed from the resource, local
+secret id, and epoch with resource-bound associated data and random nonces.
+Prototype BLAKE3-XOR private blob envelopes from earlier pre-deployment builds
+are rejected and should be recreated from plaintext.
 Later designs can add Keyhive-like convergent capabilities and BeeKEM/CGKA-style
 group key evolution. The bootstrap does not implement BeeKEM and does not claim
 strong forward secrecy or post-compromise security.

docs/command-stability.md

@@ -57,22 +57,17 @@ The following commands are tested but may still change while the subsystem
 settles:
 
 - `geth overlay status|plan|join|leave|interface-plan|up|down|peers|send|recv`
+- `geth cas add-private`
+- `geth cas get-private`
 
 Migration expectation: overlay membership records and authorization resources
 should remain readable, but packet runtime flags, platform activation details,
 and route metadata may change before the first deployment tag.
-
-## Prototype
-
-The following commands intentionally do not claim a stable security or storage
-contract yet:
-
-- `geth cas add-private`
-- `geth cas get-private`
-
-Migration expectation: prototype private CAS envelopes may be replaced by an
-audited AEAD/key-envelope design. Existing prototype blobs may need an explicit
-re-encryption or export/import workflow.
+Private CAS writes use an AES-256-GCM envelope, but the command family remains
+experimental while key envelopes, remote sharing, and forward-secrecy/PCS
+properties are explicitly out of scope. Prototype BLAKE3-XOR envelopes from
+earlier pre-deployment builds are rejected with a clear error and should be
+recreated from plaintext.
 
 ## Adding Commands
 

docs/production-readiness-roadmap.md

@@ -191,22 +191,22 @@ Goal: finish the authorization and remote-input audit before deployment.
 Goal: remove prototype cryptography from paths users may treat as real
 confidential storage.
 
-- `[ ]` Replace prototype private CAS envelope.
+- `[x]` Replace prototype private CAS envelope.
   Acceptance criteria:
-  - `[ ]` The BLAKE3-XOR prototype envelope is not used for new private CAS
+  - `[x]` The BLAKE3-XOR prototype envelope is not used for new private CAS
     writes.
-  - `[ ]` New private CAS writes use a reviewed AEAD construction or an
+  - `[x]` New private CAS writes use a reviewed AEAD construction or an
     established envelope format such as age.
-  - `[ ]` Key derivation, nonce generation, and envelope versioning are
+  - `[x]` Key derivation, nonce generation, and envelope versioning are
     documented.
-  - `[ ]` Tests cover tamper detection, wrong resource, wrong key, and nonce
+  - `[x]` Tests cover tamper detection, wrong resource, wrong key, and nonce
     uniqueness behavior.
 
-- `[ ]` Define pre-release encrypted blob migration behavior.
+- `[x]` Define pre-release encrypted blob migration behavior.
   Acceptance criteria:
-  - `[ ]` Existing prototype envelopes are either rejected with a clear error
+  - `[x]` Existing prototype envelopes are either rejected with a clear error
     or migrated through an explicit command.
-  - `[ ]` Docs state that prototype envelopes made before deployment are not a
+  - `[x]` Docs state that prototype envelopes made before deployment are not a
     durable security format.
 
 ## Phase 6: Sync Correctness And Fault Testing
@@ -343,7 +343,7 @@ Goal: prove the system works as an actual base layer before broader use.
 3. `[x]` Add stable contract and golden JSON tests.
 4. `[x]` Harden store migrations and backup.
 5. `[ ]` Complete security-boundary test coverage.
-6. `[ ]` Replace prototype private CAS cryptography.
+6. `[x]` Replace prototype private CAS cryptography.
 7. `[ ]` Add fault-injection sync tests.
 8. `[ ]` Improve automation commands and JSON errors.
 9. `[ ]` Add operational health, doctor, and release gates.

docs/roadmap.md

@@ -648,8 +648,12 @@ authorization and durable-state boundaries clear.
   - `[x]` `geth cas get-private <resource> <hash> --out <path>` decrypts with
     a matching local resource secret epoch.
   - `[x]` Access is gated by local resource secret epoch material.
-  - `[x]` Tests verify encrypted blob roundtrip and wrong resource/secret
-    rejection.
+  - `[x]` New writes use an AES-256-GCM envelope with resource-bound
+    associated data and random nonces.
+  - `[x]` Prototype BLAKE3-XOR envelopes from earlier pre-deployment builds are
+    rejected with a clear error.
+  - `[x]` Tests verify encrypted blob roundtrip, tamper detection, wrong
+    resource/secret rejection, old-envelope rejection, and nonce uniqueness.
   - `[x]` Docs explicitly avoid claiming forward secrecy or PCS.
 
 - `[x]` Iroh-docs KV integration.