diff --git a/README.md b/README.md
index 076b66f..ada05ea 100644
--- a/README.md
+++ b/README.md
@@ -11,18 +11,18 @@ and storage-agnostic.
 `requirements.txt`:
 
 ```
-envelope_crypto @ git+ssh://git@git.rethinkstudios.io/rethink-public/envelope_crypto.git@v0.1.5
+envelope_crypto @ git+ssh://git@git.rethinkstudios.io/rethink-public/envelope_crypto.git@v0.1.6
 ```
 
 Direct:
 
 ```bash
-pip install "envelope_crypto @ git+ssh://git@git.rethinkstudios.io/rethink-public/envelope_crypto.git@v0.1.5"
+pip install "envelope_crypto @ git+ssh://git@git.rethinkstudios.io/rethink-public/envelope_crypto.git@v0.1.6"
 ```
 
 Requires `cryptography` (pulled transitively).
 
-Drop the `@v0.1.5` suffix from the line above to install the latest unpinned.
+Drop the `@v0.1.6` suffix from the line above to install the latest unpinned.
 
 ## First-time setup
 
@@ -177,6 +177,18 @@ The lib never touches a database; only the caller's storage layer differs.
 - The scheme is envelope/hybrid encryption (AES-256-GCM data key wrapped by RSA-OAEP).
   Using it does not by itself confer PCI-DSS or any other compliance — that is a
   whole-system property.
+- `initialize(master_key)` requires exactly 32 bytes (`bytes`, `len == 32`) — a
+  16/24-byte key or a `str` raises `ValueError` instead of silently downgrading to
+  AES-128/192 or failing late at first encrypt.
+- Wrap/unwrap (`encrypt_aes_key_with_rsa`, `decrypt_aes_key_with_rsa`,
+  `authorize_system`, `bootstrap`, `rotate_master_key`) is **RSA-only**. A non-RSA
+  key (e.g. Ed25519/EC) loads and fingerprints fine but raises a clear `ValueError`
+  at wrap/unwrap rather than a raw `AttributeError`.
+- `fingerprint_data` serializes non-JSON-native values (datetime/date/time,
+  bytes/bytearray, ObjectId-like objects) via a stable `default=` handler instead of
+  raising `TypeError`, and type-tags dict keys internally so `{1: "a"}` and
+  `{"1": "a"}` no longer collide to the same fingerprint. Never logs the data it
+  fingerprints.
 
 ## Versioning
 
diff --git a/pyproject.toml b/pyproject.toml
index d6cb8b5..9483705 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "envelope_crypto"
-version = "0.1.5"
+version = "0.1.6"
 description = "Envelope encryption (RSA-OAEP wrapped AES-256-GCM) for dict records — config-free, storage-agnostic, installable."
 requires-python = ">=3.10"
 dependencies = [
diff --git a/src/envelope_crypto/envelope_crypto.py b/src/envelope_crypto/envelope_crypto.py
index 96e3de0..38a7cc2 100644
--- a/src/envelope_crypto/envelope_crypto.py
+++ b/src/envelope_crypto/envelope_crypto.py
@@ -1,16 +1,18 @@
 """
 envelope encryption for dict records
 
-hybrid encryption: a random AES-256-GCM data key (DEK) encrypts the data, and
-that key is wrapped (RSA-OAEP) per authorized system's public key (KEK) for
-distribution. the wrapped key is stored by the caller, keyed by fingerprint;
-each system unwraps its own copy with its private key. this is the same
-envelope-encryption pattern used by KMS-style systems.
+hybrid encryption: a random AES-256-GCM data key (DEK) encrypts the data, wrapped
+(RSA-OAEP) per authorized system's public key (KEK) for distribution. the wrapped
+key is stored by the caller, keyed by fingerprint; each system unwraps its own copy
+with its private key. same pattern KMS-style systems use. RSA-envelope only — a
+non-RSA key (e.g. Ed25519/EC) loads and fingerprints fine but raises ValueError at
+wrap/unwrap. never logs key material (DEK, PEM, wrapped key) — only fingerprints
+and counts.
 
     from envelope_crypto import EnvelopeCrypto
 
     crypto = EnvelopeCrypto()
-    crypto.initialize(master_key)                      # 32-byte AES DEK
+    crypto.initialize(master_key)                      # exactly 32 bytes (AES-256)
     enc = crypto.encrypt_data({"ssn": "..."})          # -> {secure, iv, data}
     plain = crypto.decrypt_data(enc)                   # -> original
 
@@ -32,9 +34,8 @@ authorize another system (this instance must already hold the DEK):
     fp, wrapped = crypto.authorize_system(other_pub_path)
     caller_store({"_id": fp, "key": wrapped})
 
-deauthorize: caller deletes that fingerprint's record. note this stops future
-unwraps but does not revoke a DEK already in a running system's memory — rotate
-if compromised.
+deauthorize: caller deletes that fingerprint's record. stops future unwraps but
+does not revoke a DEK already in a running system's memory — rotate if compromised.
 
 rotate (new DEK + re-encrypt): generate a new DEK, wrap for the still-authorized
 set, then re-encrypt existing records old -> new:
@@ -45,24 +46,24 @@ set, then re-encrypt existing records old -> new:
         caller_update(new_crypto.reencrypt(crypto, record))
 
 reencrypt/is_encrypted_record/decrypt_record all detect a bare {secure, iv, data}
-blob used AS the whole record (the file-storage pattern), not just blobs nested
-under a key. reencrypt fails loud (raises) rather than silently leaving a field
-under the old key — including when a blob sits deeper than `traversal_level`;
-is_encrypted_record falls back to an unbounded-depth scan past traversal_level so
-it reliably catches leftovers as a post-rotation audit.
+blob used AS the whole record (file-storage pattern), not just blobs nested under a
+key. reencrypt fails loud (raises) rather than silently leaving a field under the
+old key — including a blob nested deeper than `traversal_level`; is_encrypted_record
+falls back to an unbounded-depth scan past traversal_level to reliably catch
+leftovers as a post-rotation audit.
 
 config-free: the host supplies the DEK and RSA key paths; this lib never imports
 config, configures logging, or touches a database. storage-agnostic — the
 encrypted blob is a plain dict; store it in mongo, a sql json column, or a file.
 
-encrypt_data/decrypt_data round-trip a dict only when every key is a str —
-json (the wire format under the hood) has no other key type, so encrypt_data
-raises TypeError on a non-str key (e.g. an int-keyed dict of discord snowflakes)
-rather than silently stringifying it and losing the original key on decrypt.
+encrypt_data/decrypt_data round-trip a dict only when every key is a str — json
+(the wire format) has no other key type, so encrypt_data raises TypeError on a
+non-str key (e.g. an int-keyed dict of discord snowflakes) rather than silently
+stringifying it and losing the original key on decrypt.
 
 naming: EnvelopeCrypto is canonical. PCICrypto / DocumentCrypto / RecordCrypto are
-aliases (PCICrypto is a deprecated legacy alias). the document/record/dict
-function variants are the same functions — use whichever fits your storage.
+aliases (PCICrypto is a deprecated legacy alias). the document/record/dict function
+variants are the same functions — use whichever fits your storage.
 """
 
 import os
@@ -75,19 +76,31 @@ from typing import Any, Dict, List, Optional, Tuple, Union
 
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.primitives import hashes, serialization
-from cryptography.hazmat.primitives.asymmetric import padding
+from cryptography.hazmat.primitives.asymmetric import padding, rsa
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM
 from cryptography.hazmat.primitives.serialization import load_ssh_public_key
 
 _log = logging.getLogger(__name__)
 
 
-def _load_private_key(key_data: bytes, pw: Optional[bytes]):
-    """load a PEM or OpenSSH private key, normalizing the missing-password error
+def _password_mismatch_message(pw: Optional[bytes]) -> str:
+    """clear ValueError text for a TypeError raised by a password/encryption mismatch
 
-    cryptography raises TypeError when a key is encrypted but no password was given
-    (PEM raises it on the first call; OpenSSH raises it inside the openssh fallback).
-    both are normalized to a clear ValueError so callers see one error type.
+    cryptography raises TypeError for both directions: encrypted key + no password,
+    and unencrypted key + a password given. branch on which the caller supplied so
+    the message matches the actual case instead of always claiming "encrypted".
+    """
+    if pw is not None:
+        return "password was given but private key is not encrypted"
+    return "private key is encrypted but no password was provided"
+
+
+def _load_private_key(key_data: bytes, pw: Optional[bytes]):
+    """load a PEM or OpenSSH private key, normalizing the password/encryption mismatch error
+
+    cryptography raises TypeError for a password/encryption mismatch (PEM raises it on
+    the first call; OpenSSH raises it inside the openssh fallback), normalized here to a
+    clear ValueError so callers see one error type with a message matching the actual case.
     """
     try:
         return serialization.load_pem_private_key(key_data, password=pw)
@@ -96,18 +109,14 @@ def _load_private_key(key_data: bytes, pw: Optional[bytes]):
             try:
                 return serialization.load_ssh_private_key(key_data, password=pw)
             except TypeError as ssh_error:
-                raise ValueError(
-                    "private key is encrypted but no password was provided"
-                ) from ssh_error
+                raise ValueError(_password_mismatch_message(pw)) from ssh_error
         if pw is not None:
             # a password was given but the PEM load still failed — most likely a wrong
             # password; give a clearer message than cryptography's raw "Bad decrypt"
             raise ValueError("could not load private key (wrong password or malformed key)") from error
         raise error
     except TypeError as error:
-        raise ValueError(
-            "private key is encrypted but no password was provided"
-        ) from error
+        raise ValueError(_password_mismatch_message(pw)) from error
 
 
 def _fingerprint_of(public_key) -> str:
@@ -143,6 +152,18 @@ def _has_encrypted_field(record: Any) -> bool:
     return any(_has_encrypted_field(value) for value in record.values())
 
 
+def _require_rsa(key) -> None:
+    """raise ValueError unless key is an RSA public or private key
+
+    this lib is RSA-envelope only: get_rsa_key_fingerprint accepts any key type
+    (fingerprinting is algorithm-agnostic), but wrap/unwrap calls RSA-OAEP methods
+    that don't exist on e.g. Ed25519/EC keys and would otherwise crash raw with an
+    AttributeError far from a clear cause.
+    """
+    if not isinstance(key, (rsa.RSAPublicKey, rsa.RSAPrivateKey)):
+        raise ValueError(f"RSA key required for envelope wrap/unwrap, got {type(key).__name__}")
+
+
 def _load_public_key(key_data: bytes):
     """load a PEM or OpenSSH public key, normalizing non-key input to ValueError
 
@@ -190,14 +211,11 @@ class EnvelopeCrypto:
     ) -> bool:
         """verify the full pipeline against a keypair; raises on any mismatch
 
-        round-trips sample data through this instance's DEK, then wraps the DEK
-        with the public key and unwraps with the private key, confirming they
-        match. run after bootstrap (or anytime as a health check) to catch a bad
-        keypair or wrong key path before relying on it. is_file (default True) is
-        threaded through to both the public and private key loads, so
-        is_file=False correctly treats both rsa_public_key and rsa_private_key as
-        in-memory PEM/OpenSSH data rather than opening either as a file path.
-        returns True on success.
+        round-trips sample data through this instance's DEK, then wraps and unwraps
+        the DEK with the given keypair, confirming they match. run after bootstrap
+        (or as a health check) to catch a bad keypair or wrong path before relying
+        on it. is_file threads through to both key loads (is_file=False treats both
+        as in-memory PEM/OpenSSH data, not paths). returns True on success.
         """
         if not self.master_key:
             raise ValueError("self_test: not initialized with a key")
@@ -221,7 +239,15 @@ class EnvelopeCrypto:
         return True
 
     def initialize(self, master_key: bytes) -> None:
-        """arm the instance with the AES data key (DEK)"""
+        """arm the instance with the AES data key (DEK)
+
+        requires exactly 32 bytes (AES-256): a shorter key would silently downgrade
+        to AES-128/192 with no warning, and a non-bytes value would otherwise fail
+        late and opaquely at first encrypt/decrypt — both rejected here instead.
+        never logs the key material itself.
+        """
+        if not isinstance(master_key, bytes) or len(master_key) != 32:
+            raise ValueError("master_key must be exactly 32 bytes (AES-256)")
         self.master_key = master_key
         _log.info("crypto initialized with data key")
 
@@ -248,11 +274,10 @@ class EnvelopeCrypto:
         """return a base64 SHA-256 fingerprint of an RSA key for identification
 
         for an encrypted private key (is_private=True), pass its `password`; an
-        unencrypted key ignores it. fingerprinting always uses the public half, so a
-        private and its public key produce the same fingerprint. PEM and OpenSSH
-        private-key formats are both accepted (mirrors decrypt_aes_key_with_rsa). an
-        encrypted key with no/wrong password raises ValueError with a clear message
-        (cryptography raises TypeError for the missing-password case — normalized here).
+        unencrypted key ignores it. always fingerprints the public half, so a
+        private key and its public key match. PEM and OpenSSH accepted (mirrors
+        decrypt_aes_key_with_rsa). a password/encryption mismatch raises a clear
+        ValueError (cryptography's raw TypeError normalized here).
         """
         if is_file:
             with open(key_path_or_data, "rb") as key_file:
@@ -278,7 +303,11 @@ class EnvelopeCrypto:
     def encrypt_aes_key_with_rsa(
         self, aes_key: bytes, rsa_key: str, is_file: bool = True
     ) -> Tuple[str, str]:
-        """wrap an AES key with an RSA public key; returns (fingerprint, wrapped_b64)"""
+        """wrap an AES key with an RSA public key; returns (fingerprint, wrapped_b64)
+
+        raises ValueError if rsa_key is not an RSA key (this lib is RSA-envelope only;
+        e.g. an Ed25519/EC key loads and fingerprints fine but cannot wrap).
+        """
         if is_file:
             with open(rsa_key, "rb") as key_file:
                 key_data = key_file.read()
@@ -286,6 +315,7 @@ class EnvelopeCrypto:
             key_data = rsa_key.encode() if isinstance(rsa_key, str) else rsa_key
 
         public_key = _load_public_key(key_data)
+        _require_rsa(public_key)
 
         wrapped = public_key.encrypt(
             aes_key,
@@ -319,6 +349,7 @@ class EnvelopeCrypto:
             key_data = rsa_private_key.encode() if isinstance(rsa_private_key, str) else rsa_private_key
         pw = password.encode() if password else None
         private_key = _load_private_key(key_data, pw)
+        _require_rsa(private_key)
 
         wrapped = base64.b64decode(encrypted_key_base64)
         aes_key = private_key.decrypt(
@@ -399,17 +430,14 @@ class EnvelopeCrypto:
     def decrypt_data(self, encrypted_data: Dict[str, str]) -> Union[Dict[str, Any], str]:
         """decrypt a {secure, iv, data} blob; returns the original dict or string
 
-        `encrypt_data` only json-encodes dicts (a string is stored verbatim), so decrypt
-        only treats a json-OBJECT plaintext as a dict and returns everything else as the
-        raw string. this keeps the type faithful for the common cases: a string that is
-        json-shaped but NOT an object ('123'->'123', 'true'->'true', '[1,2]'->'[1,2]')
-        round-trips as a STRING, not an int/bool/list. the one irreducible ambiguity: a
-        string whose exact value is a json OBJECT ('{"a":1}') decrypts to a dict, because
-        without a type marker it is indistinguishable from a stored dict — don't store a
-        bare string that is a json object if you need it back as a string. existing stored
-        blobs are unaffected — a dict was stored as a json object and still parses to a dict.
-        dict KEYS round-trip faithfully only because encrypt_data now requires str keys —
-        json has no other key type, so this is the only shape decrypt_data ever sees.
+        encrypt_data only json-encodes dicts (a string is stored verbatim), so decrypt
+        treats a json-OBJECT plaintext as a dict and everything else as a raw string —
+        a json-shaped but non-object string ('123', 'true', '[1,2]') round-trips as a
+        STRING, not int/bool/list. one irreducible ambiguity: a string whose exact
+        value is a json object ('{"a":1}') decrypts to a dict, indistinguishable
+        without a type marker from a stored dict — don't store a bare json-object
+        string if you need it back as a string. dict keys round-trip faithfully
+        because encrypt_data requires str keys (json's only key type).
         """
         if not self.master_key:
             raise ValueError("not initialized with data key")
@@ -431,26 +459,22 @@ class EnvelopeCrypto:
     def reencrypt(self, source_crypto: "EnvelopeCrypto", record: dict, traversal_level: int = 2) -> dict:
         """re-encrypt a record's encrypted fields from source_crypto's key to this one's
 
-        self holds the destination (new) key; source_crypto holds the source (old)
-        key. only {secure, iv, data} fields are touched; plaintext fields are left
-        as-is. returns a new dict; the input is not mutated. used during rotation.
+        self holds the destination (new) key; source_crypto holds the source (old) key.
+        only {secure, iv, data} fields are touched; plaintext fields are left as-is.
+        returns a new dict; the input is not mutated. used during rotation. if `record`
+        itself is a bare blob (file-storage pattern) it is re-encrypted directly and
+        returned in place of `record`, not nested under a key.
 
-        if `record` itself is a {secure, iv, data} blob (the file-storage pattern, where
-        the blob IS the whole document) it is re-encrypted directly and the result is
-        returned in place of `record` — not nested under a key.
+        fails loud, unlike decrypt_record: a per-field decrypt failure RAISES (silently
+        keeping a field under the old key would lose it once that key is retired), and
+        so does a blob nested DEEPER than `traversal_level` — raise a higher
+        traversal_level or flatten the record before rotation instead.
 
-        unlike decrypt_record (which logs a failed field and leaves it encrypted), a
-        per-field decrypt failure here RAISES — rotation must fail loud, since silently
-        keeping a field under the old key would lose it once the old key is retired. for
-        the same reason, a blob nested DEEPER than `traversal_level` also RAISES instead
-        of being silently left under the old key: the caller either needs a higher
-        `traversal_level` or must flatten the record before rotation.
-
-        traversal recurses into nested DICTS only; a blob nested inside a LIST is NOT
-        re-encrypted and is NOT covered by the depth-limit raise above. records in this
-        scheme key blobs by field name, not inside arrays, so this doesn't arise in
-        practice — but if you store list-nested blobs, flatten them to dict fields before
-        rotation or they'll be silently left under the old key.
+        traversal recurses into nested DICTS only; a blob nested inside a LIST is not
+        re-encrypted and not covered by the depth-limit raise. this scheme keys blobs
+        by field name, not inside arrays, so this shouldn't arise in practice — but
+        flatten list-nested blobs to dict fields before rotation or they'll be
+        silently left under the old key.
         """
         if not self.master_key:
             raise ValueError("destination not initialized with data key")
@@ -484,12 +508,11 @@ def is_encrypted_record(record, traversal_level: int = 2) -> bool:
     """return whether a record has any encrypted ({secure, iv, data}) fields
 
     checks `record` itself (the file-storage pattern stores the blob AS the whole
-    document, not nested under a key) as well as fields up to `traversal_level` deep.
-    beyond that bounded pass, this ALSO does an unbounded-depth scan before giving up —
-    so a blob left behind by a shallower decrypt_record/reencrypt call (nested deeper
-    than their traversal_level) is still reported as encrypted. this makes the function
-    safe to use as a leftover-detecting post-rotation audit: it never returns False for
-    a record that still contains a blob, at any depth.
+    document) as well as fields up to `traversal_level` deep. beyond that bounded
+    pass, falls back to an unbounded-depth scan, so a blob left behind by a
+    shallower decrypt_record/reencrypt call is still reported — safe to use as a
+    leftover-detecting post-rotation audit; never returns False for a record that
+    still contains a blob, at any depth.
 
     aliases: is_encrypted_document, is_encrypted_dict — same function
     """
@@ -515,14 +538,10 @@ def is_encrypted_record(record, traversal_level: int = 2) -> bool:
 def decrypt_record(crypto: EnvelopeCrypto, record, traversal_level: int = 2) -> Union[dict, Any]:
     """decrypt a record's encrypted fields into a new dict (up to traversal_level deep)
 
-    if `record` itself is a {secure, iv, data} blob (the file-storage pattern, where the
-    blob IS the whole document) it is decrypted directly and the decrypted value
-    (dict or string — see decrypt_data) is returned in place of `record`.
-
-    failures on a single field are logged and that field is left encrypted, so a
-    partial failure is visible (the {secure,...} blob remains) rather than silent. a
-    failure decrypting `record` itself (the self-blob case above) is likewise logged
-    and the still-encrypted blob is returned unchanged.
+    if `record` itself is a bare {secure, iv, data} blob (file-storage pattern) it is
+    decrypted directly and the value (dict or string — see decrypt_data) is returned
+    in place of `record`. a failure on a single field (or on `record` itself) is
+    logged and left encrypted, so a partial failure stays visible rather than silent.
 
     aliases: decrypt_document, decrypt_dict — same function
     """
@@ -550,9 +569,49 @@ def decrypt_record(crypto: EnvelopeCrypto, record, traversal_level: int = 2) ->
     return result
 
 
+def _fingerprint_default(value: Any) -> str:
+    """json.dumps default= handler for values fingerprint_data can't natively serialize
+
+    covers datetime/date/time (isoformat), bytes/bytearray (hex), and anything else
+    (e.g. ObjectId) via a type-tagged repr — never raises, never logs the value.
+    """
+    if hasattr(value, "isoformat"):
+        return f"isoformat:{value.isoformat()}"
+    if isinstance(value, (bytes, bytearray)):
+        return f"hex:{value.hex()}"
+    return f"{type(value).__name__}:{value!r}"
+
+
+def _fingerprint_normalize(value: Any) -> Any:
+    """recursively tag dict keys with their type to avoid cross-type key collisions
+
+    json object keys are always strings, so {1: "a"} and {"1": "a"} would otherwise
+    serialize identically and collide to the same fingerprint; prefixing each key with
+    its type name keeps them distinct. non-dict containers/values pass through
+    untouched (lists recurse; leaf values are handled by _fingerprint_default).
+    """
+    if isinstance(value, dict):
+        return {
+            f"{type(key).__name__}:{key!r}": _fingerprint_normalize(sub_value)
+            for key, sub_value in value.items()
+        }
+    if isinstance(value, (list, tuple)):
+        return [_fingerprint_normalize(item) for item in value]
+    return value
+
+
 def fingerprint_data(data: dict) -> str:
-    """return a deterministic SHA-256 hex fingerprint of a dict"""
-    return hashlib.sha256(json.dumps(data, sort_keys=True).encode()).hexdigest()
+    """return a deterministic, collision-free SHA-256 hex fingerprint of a dict
+
+    dict keys of different types that would otherwise coerce to the same JSON string
+    (e.g. {1: "a"} vs {"1": "a"}) are kept distinct via a type-tagged pre-pass. values
+    that aren't JSON-native (datetime/date/time, bytes/bytearray, ObjectId-like
+    objects) are serialized via a stable default= handler instead of raising. never
+    logs the data being fingerprinted.
+    """
+    normalized = _fingerprint_normalize(data)
+    encoded = json.dumps(normalized, sort_keys=True, default=_fingerprint_default)
+    return hashlib.sha256(encoded.encode()).hexdigest()
 
 
 # function aliases — same functions, naming preference only