Delete the keychain item or Secure Enclave key of a failed unlocker add (closes #89)

A Secure Enclave unlocker add gets the long-term key before it creates
the Secure Enclave key, so a wrong passphrase creates none, and deletes
the key if a later step fails. macse.CreateKey finds the new key's hash
right after sc_auth creates it, failing with an error naming the label
if it cannot, and deletes the key if getting its public key then fails.
A keychain unlocker add writes all of the unlocker's files before it
stores the keychain item, and deletes the item if moving the unlocker
into place then fails. A failure to delete is reported along with the
original error.

The Objective-C and macse_darwin.go were only read, never compiled or
run; the new tests run only on a Mac.

Model: opus-5-5

internal/macse/macse_darwin.go

@@ -15,6 +15,7 @@ package macse
 import "C"
 
 import (
+	"errors"
 	"fmt"
 	"unsafe"
 )
@@ -39,10 +40,9 @@ const (
 
 // CreateKey creates a new P-256 non-exportable key in the Secure Enclave via sc_auth.
 // Returns the uncompressed public key bytes (65 bytes) and the identity hash
-// (for deletion).
+// (for deletion). If getting the public key fails, CreateKey deletes the key
+// again; a failure to delete is returned along with the first error.
 func CreateKey(label string) (publicKey []byte, hash string, err error) {
-	pubKeyBuf := make([]C.uint8_t, p256UncompressedKeySize)
-	pubKeyLen := C.int(p256UncompressedKeySize)
 	var hashBuf [hashBufferSize]C.char
 	var errBuf [errorBufferSize]C.char
 
@@ -50,7 +50,6 @@ func CreateKey(label string) (publicKey []byte, hash string, err error) {
 	defer C.free(unsafe.Pointer(cLabel)) //nolint:nlreturn // CGo free pattern
 
 	result := C.se_create_key(cLabel,
-		&pubKeyBuf[0], &pubKeyLen,
 		&hashBuf[0], C.int(hashBufferSize),
 		&errBuf[0], C.int(errorBufferSize))
 
@@ -58,9 +57,29 @@ func CreateKey(label string) (publicKey []byte, hash string, err error) {
 		return nil, "", fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
 	}
 
+	h := C.GoString(&hashBuf[0])
+
+	pubKeyBuf := make([]C.uint8_t, p256UncompressedKeySize)
+	pubKeyLen := C.int(p256UncompressedKeySize)
+
+	result = C.se_copy_public_key(cLabel,
+		&pubKeyBuf[0], &pubKeyLen,
+		&errBuf[0], C.int(errorBufferSize))
+
+	if result != 0 {
+		err = fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
+
+		deleteErr := DeleteKey(h)
+		if deleteErr != nil {
+			err = errors.Join(err,
+				fmt.Errorf("failed to delete key %s: %w", label, deleteErr))
+		}
+
+		return nil, "", err
+	}
+
 	//nolint:nlreturn // CGo result extraction
 	pk := C.GoBytes(unsafe.Pointer(&pubKeyBuf[0]), pubKeyLen)
-	h := C.GoString(&hashBuf[0])
 
 	return pk, h, nil
 }

internal/macse/secure_enclave.h

@@ -5,20 +5,30 @@
 
 #include <stdint.h>
 
-// se_create_key creates a new P-256 key in the Secure Enclave via sc_auth.
+// se_create_key creates a new P-256 key in the Secure Enclave via sc_auth and
+// finds its identity hash. If the hash cannot be found, the key exists but
+// se_create_key fails, with an error naming the label.
 // label: unique identifier for the CTK identity (UTF-8 C string)
-// pub_key_out: output buffer for the uncompressed public key (65 bytes for P-256)
-// pub_key_len: on input, size of pub_key_out; on output, actual size written
 // hash_out: output buffer for the identity hash (for deletion)
 // hash_out_len: size of hash_out buffer
 // error_out: output buffer for error message
 // error_out_len: size of error_out buffer
 // Returns 0 on success, -1 on failure.
 int se_create_key(const char *label,
-                  uint8_t *pub_key_out, int *pub_key_len,
                   char *hash_out, int hash_out_len,
                   char *error_out, int error_out_len);
 
+// se_copy_public_key copies the public key of a CTK identity.
+// label: label of the CTK identity
+// pub_key_out: output buffer for the uncompressed public key (65 bytes for P-256)
+// pub_key_len: on input, size of pub_key_out; on output, actual size written
+// error_out: output buffer for error message
+// error_out_len: size of error_out buffer
+// Returns 0 on success, -1 on failure.
+int se_copy_public_key(const char *label,
+                       uint8_t *pub_key_out, int *pub_key_len,
+                       char *error_out, int error_out_len);
+
 // se_encrypt encrypts data using the SE-backed public key (ECIES).
 // label: label of the CTK identity whose public key to use
 // plaintext: data to encrypt

internal/macse/secure_enclave.m

@@ -47,7 +47,6 @@ static SecKeyRef lookup_ctk_private_key(const char *label, char *error_out, int
 }
 
 int se_create_key(const char *label,
-                  uint8_t *pub_key_out, int *pub_key_len,
                   char *hash_out, int hash_out_len,
                   char *error_out, int error_out_len) {
     @autoreleasepool {
@@ -87,7 +86,56 @@ int se_create_key(const char *label,
             return -1;
         }
 
-        // Retrieve the public key from the created identity
+        // Get the identity hash, which deleting the key needs, by parsing
+        // sc_auth list output
+        hash_out[0] = '\0';
+        NSTask *listTask = [[NSTask alloc] init];
+        listTask.executableURL = [NSURL fileURLWithPath:@"/usr/sbin/sc_auth"];
+        listTask.arguments = @[@"list-ctk-identities"];
+
+        NSPipe *listPipe = [NSPipe pipe];
+        listTask.standardOutput = listPipe;
+        listTask.standardError = [NSPipe pipe];
+
+        if ([listTask launchAndReturnError:&nsError]) {
+            [listTask waitUntilExit];
+            NSData *listData = [listPipe.fileHandleForReading readDataToEndOfFile];
+            NSString *listStr = [[NSString alloc] initWithData:listData
+                                                      encoding:NSUTF8StringEncoding];
+
+            for (NSString *line in [listStr componentsSeparatedByString:@"\n"]) {
+                if ([line containsString:labelStr]) {
+                    NSMutableArray *tokens = [NSMutableArray array];
+                    for (NSString *part in [line componentsSeparatedByCharactersInSet:
+                                            [NSCharacterSet whitespaceCharacterSet]]) {
+                        if (part.length > 0) {
+                            [tokens addObject:part];
+                        }
+                    }
+                    if (tokens.count > 1) {
+                        snprintf(hash_out, hash_out_len, "%s", [tokens[1] UTF8String]);
+                    }
+                    break;
+                }
+            }
+        }
+
+        if (hash_out[0] == '\0') {
+            NSString *msg = [NSString stringWithFormat:
+                             @"created key '%s' but found no hash for it in sc_auth list-ctk-identities",
+                             label];
+            snprintf_error(error_out, error_out_len, msg);
+            return -1;
+        }
+
+        return 0;
+    }
+}
+
+int se_copy_public_key(const char *label,
+                       uint8_t *pub_key_out, int *pub_key_len,
+                       char *error_out, int error_out_len) {
+    @autoreleasepool {
         SecKeyRef privateKey = lookup_ctk_private_key(label, error_out, error_out_len);
         if (!privateKey) {
             return -1;
@@ -126,39 +174,6 @@ int se_create_key(const char *label,
         *pub_key_len = (int)length;
         CFRelease(pubKeyData);
 
-        // Get the identity hash by parsing sc_auth list output
-        hash_out[0] = '\0';
-        NSTask *listTask = [[NSTask alloc] init];
-        listTask.executableURL = [NSURL fileURLWithPath:@"/usr/sbin/sc_auth"];
-        listTask.arguments = @[@"list-ctk-identities"];
-
-        NSPipe *listPipe = [NSPipe pipe];
-        listTask.standardOutput = listPipe;
-        listTask.standardError = [NSPipe pipe];
-
-        if ([listTask launchAndReturnError:&nsError]) {
-            [listTask waitUntilExit];
-            NSData *listData = [listPipe.fileHandleForReading readDataToEndOfFile];
-            NSString *listStr = [[NSString alloc] initWithData:listData
-                                                      encoding:NSUTF8StringEncoding];
-
-            for (NSString *line in [listStr componentsSeparatedByString:@"\n"]) {
-                if ([line containsString:labelStr]) {
-                    NSMutableArray *tokens = [NSMutableArray array];
-                    for (NSString *part in [line componentsSeparatedByCharactersInSet:
-                                            [NSCharacterSet whitespaceCharacterSet]]) {
-                        if (part.length > 0) {
-                            [tokens addObject:part];
-                        }
-                    }
-                    if (tokens.count > 1) {
-                        snprintf(hash_out, hash_out_len, "%s", [tokens[1] UTF8String]);
-                    }
-                    break;
-                }
-            }
-        }
-
         return 0;
     }
 }