diff --git a/docs/getting-started/operations.md b/docs/getting-started/operations.md
index 3f8b6537..b692794b 100644
--- a/docs/getting-started/operations.md
+++ b/docs/getting-started/operations.md
@@ -60,7 +60,7 @@ A Web restart, including one caused by `oac apply`, signs everyone out of the co
 
 ## Core key
 
-Each installation has one administrator credential, the Core key. The installer generates a 64-character random key in `data/secrets/web/core.key`. Read it with `oac core-key --show`; the file is owned by the container user. The Core key:
+Each installation has one administrator credential, the Core key. The installer generates a key with the `oac_admin_` prefix followed by 64 random lowercase hexadecimal characters in `data/secrets/web/core.key`. Read it with `oac core-key --show`; the file is owned by the container user. The Core key:
 
 - signs in to Web. The browser gets an HttpOnly session cookie, never the key;
 - authorizes Core API (`/core/v1`) requests sent as `Authorization: Bearer <Core key>`;
diff --git a/docs/zh/getting-started/operations.md b/docs/zh/getting-started/operations.md
index 4a3755df..facb1309 100644
--- a/docs/zh/getting-started/operations.md
+++ b/docs/zh/getting-started/operations.md
@@ -1,7 +1,7 @@
 ---
 title: "管理你的安装"
 source: docs/getting-started/operations.md
-source_hash: e87c7a1e577b8732929bb1c1fead1d54abfe6b607d8c4aed43faf38dca405ed5
+source_hash: e60a6e96cd61692b6adc7664874ba0ed2ce489982e7da2fe2347631ee2a94c0a
 ---
 
 安装运维人员负责 Core 主机、存储和可用性。节点主机运行各自的服务；参阅[节点](nodes.md)。设置见[配置参考](../configuration.md)。
@@ -62,7 +62,7 @@ Web 重启（包括 `oac apply` 引起的重启）会让所有控制台用户退
 
 ## Core 密钥 {#core-key}
 
-每个安装有一个管理员凭据，即 Core 密钥。安装程序在 `data/secrets/web/core.key` 生成 64 字符随机密钥。用 `oac core-key --show` 读取；该文件属于容器用户。Core 密钥：
+每个安装有一个管理员凭据，即 Core 密钥。安装程序在 `data/secrets/web/core.key` 生成以 `oac_admin_` 为前缀、后接 64 个随机小写十六进制字符的密钥。用 `oac core-key --show` 读取；该文件属于容器用户。Core 密钥：
 
 - 用于登录 Web。浏览器获得 HttpOnly 会话 cookie，不持有密钥；
 - 通过 `Authorization: Bearer <Core key>` 授权 Core API（`/core/v1`）请求；
diff --git a/services/core/cmd/oac/init.go b/services/core/cmd/oac/init.go
index 3d9f3a68..bb5a5405 100644
--- a/services/core/cmd/oac/init.go
+++ b/services/core/cmd/oac/init.go
@@ -254,7 +254,13 @@ func initialize(root string, release releaseIdentity, fetch func() (map[string][
 		name     string
 		generate func() string
 	}{
-		{"secrets/web/core.key", func() string { return randomHex(32) }},
+		{"secrets/web/core.key", func() string {
+			key, err := generateCoreKey()
+			if err != nil {
+				panic(err)
+			}
+			return key
+		}},
 		{"secrets/database/password", func() string { return randomHex(32) }},
 		{"secrets/core/credential.key", func() string { return base64.StdEncoding.EncodeToString(randomBytes(32)) }},
 		{"secrets/core/installation.id", func() string { return uuid.NewString() }},
diff --git a/services/core/cmd/oac/init_test.go b/services/core/cmd/oac/init_test.go
index 69a9c7d4..c4b89db7 100644
--- a/services/core/cmd/oac/init_test.go
+++ b/services/core/cmd/oac/init_test.go
@@ -67,9 +67,7 @@ func TestInitializeKeepsIdentityAndKeysAcrossRestarts(t *testing.T) {
 	}
 	saved := snapshot(t, root)
 	key := strings.TrimSpace(saved["secrets/web/core.key"])
-	if len(key) != 64 {
-		t.Fatalf("core key has %d characters", len(key))
-	}
+	assertCoreKeyFormat(t, key)
 	var digests []string
 	if err := json.Unmarshal([]byte(saved["secrets/core/core-key-digests.json"]), &digests); err != nil || len(digests) != 1 || digests[0] != keyDigest(key) {
 		t.Fatalf("digests = %v, %v", digests, err)
diff --git a/services/core/cmd/oac/main.go b/services/core/cmd/oac/main.go
index f18683d9..e2159239 100644
--- a/services/core/cmd/oac/main.go
+++ b/services/core/cmd/oac/main.go
@@ -115,12 +115,19 @@ func coreKeyCommand(ctx context.Context, in installation, runner Runner, args []
 	return errors.New("Usage: oac core-key [--show]")
 }
 
-func rotateCoreKey(ctx context.Context, in installation, runner Runner) error {
+func generateCoreKey() (string, error) {
 	buf := make([]byte, 32)
 	if _, err := rand.Read(buf); err != nil {
+		return "", err
+	}
+	return "oac_admin_" + hex.EncodeToString(buf), nil
+}
+
+func rotateCoreKey(ctx context.Context, in installation, runner Runner) error {
+	key, err := generateCoreKey()
+	if err != nil {
 		return err
 	}
-	key := hex.EncodeToString(buf)
 	keyPath := filepath.Join(in.data, "secrets", "web", "core.key")
 	digestPath := filepath.Join(in.data, "secrets", "core", "core-key-digests.json")
 	if err := writeSecret(keyPath, key+"\n"); err != nil {
diff --git a/services/core/cmd/oac/oac_test.go b/services/core/cmd/oac/oac_test.go
index fb2789c1..ee865c21 100644
--- a/services/core/cmd/oac/oac_test.go
+++ b/services/core/cmd/oac/oac_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 )
@@ -53,6 +54,7 @@ func TestRotateCoreKeyDigestDoesNotEchoTheKey(t *testing.T) {
 		t.Fatal(err)
 	}
 	key := strings.TrimSpace(string(raw))
+	assertCoreKeyFormat(t, key)
 	digest, err := os.ReadFile(filepath.Join(in.data, "secrets", "core", "core-key-digests.json"))
 	if err != nil || !strings.Contains(string(digest), keyDigest(key)) || strings.Contains(string(digest), key) {
 		t.Fatalf("digest %s key leaked %v", digest, err)
@@ -70,3 +72,10 @@ func (s scriptedRunner) Run(_ context.Context, args ...string) error { return s.
 func (s scriptedRunner) Output(context.Context, ...string) ([]byte, error) {
 	return nil, nil
 }
+
+func assertCoreKeyFormat(t *testing.T, key string) {
+	t.Helper()
+	if !regexp.MustCompile(`^oac_admin_[0-9a-f]{64}$`).MatchString(key) {
+		t.Fatal("core key must have the oac_admin_ prefix and 64 lowercase hexadecimal characters")
+	}
+}
diff --git a/services/web/auth.go b/services/web/auth.go
index 36bc2dac..16f23f64 100644
--- a/services/web/auth.go
+++ b/services/web/auth.go
@@ -18,7 +18,7 @@ const sessionCookie = "core_console_session"
 const sessionLifetime = 12 * time.Hour
 
 // minimumCoreKeyLength keeps guessing infeasible even though a correct key is
-// never rate limited. Installer-generated keys have 64 characters.
+// never rate limited. Installer-generated keys carry 256 bits of random entropy.
 const minimumCoreKeyLength = 32
 
 // consoleAuth signs the browser in with the Core key. Sessions live only in