diff --git a/libs/common/src/enums/feature-flag.enum.ts b/libs/common/src/enums/feature-flag.enum.ts
index 09708859ac8..fa776285ead 100644
--- a/libs/common/src/enums/feature-flag.enum.ts
+++ b/libs/common/src/enums/feature-flag.enum.ts
@@ -39,6 +39,7 @@ export enum FeatureFlag {
   PrivateKeyRegeneration = "pm-12241-private-key-regeneration",
   UserKeyRotationV2 = "userkey-rotation-v2",
   PM4154_BulkEncryptionService = "PM-4154-bulk-encryption-service",
+  PM17987_BlockType0 = "pm-17987-block-type-0",
 
   /* Tools */
   ItemShare = "item-share",
@@ -121,6 +122,7 @@ export const DefaultFeatureFlagValue = {
   [FeatureFlag.PrivateKeyRegeneration]: FALSE,
   [FeatureFlag.UserKeyRotationV2]: FALSE,
   [FeatureFlag.PM4154_BulkEncryptionService]: FALSE,
+  [FeatureFlag.PM17987_BlockType0]: FALSE,
 
   /* Platform */
   [FeatureFlag.IpcChannelFramework]: FALSE,
diff --git a/libs/common/src/key-management/crypto/services/encrypt.service.implementation.ts b/libs/common/src/key-management/crypto/services/encrypt.service.implementation.ts
index d10061a2be8..10d29198ada 100644
--- a/libs/common/src/key-management/crypto/services/encrypt.service.implementation.ts
+++ b/libs/common/src/key-management/crypto/services/encrypt.service.implementation.ts
@@ -19,10 +19,17 @@ import {
   SymmetricCryptoKey,
 } from "@bitwarden/common/platform/models/domain/symmetric-crypto-key";
 
+import {
+  DefaultFeatureFlagValue,
+  FeatureFlag,
+  getFeatureFlagValue,
+} from "../../../enums/feature-flag.enum";
 import { ServerConfig } from "../../../platform/abstractions/config/server-config";
 import { EncryptService } from "../abstractions/encrypt.service";
 
 export class EncryptServiceImplementation implements EncryptService {
+  private blockType0: boolean = DefaultFeatureFlagValue[FeatureFlag.PM17987_BlockType0];
+
   constructor(
     protected cryptoFunctionService: CryptoFunctionService,
     protected logService: LogService,
@@ -31,7 +38,7 @@ export class EncryptServiceImplementation implements EncryptService {
 
   // Handle updating private properties to turn on/off feature flags.
   onServerConfigChange(newConfig: ServerConfig): void {
-    return;
+    this.blockType0 = getFeatureFlagValue(newConfig, FeatureFlag.PM17987_BlockType0);
   }
 
   async encrypt(plainValue: string | Uint8Array, key: SymmetricCryptoKey): Promise<EncString> {
@@ -39,6 +46,12 @@ export class EncryptServiceImplementation implements EncryptService {
       throw new Error("No encryption key provided.");
     }
 
+    if (this.blockType0) {
+      if (key.encType === EncryptionType.AesCbc256_B64 || key.key.byteLength < 64) {
+        throw new Error("Type 0 encryption is not supported.");
+      }
+    }
+
     if (plainValue == null) {
       return Promise.resolve(null);
     }
@@ -70,6 +83,12 @@ export class EncryptServiceImplementation implements EncryptService {
       throw new Error("No encryption key provided.");
     }
 
+    if (this.blockType0) {
+      if (key.encType === EncryptionType.AesCbc256_B64 || key.key.byteLength < 64) {
+        throw new Error("Type 0 encryption is not supported.");
+      }
+    }
+
     const innerKey = key.inner();
     if (innerKey.type === EncryptionType.AesCbc256_HmacSha256_B64) {
       const encValue = await this.aesEncrypt(plainValue, innerKey);
diff --git a/libs/common/src/key-management/crypto/services/encrypt.service.spec.ts b/libs/common/src/key-management/crypto/services/encrypt.service.spec.ts
index 275fd266f84..c65c78d88d7 100644
--- a/libs/common/src/key-management/crypto/services/encrypt.service.spec.ts
+++ b/libs/common/src/key-management/crypto/services/encrypt.service.spec.ts
@@ -10,6 +10,8 @@ import { SymmetricCryptoKey } from "@bitwarden/common/platform/models/domain/sym
 import { CsprngArray } from "@bitwarden/common/types/csprng";
 
 import { makeStaticByteArray } from "../../../../spec";
+import { DefaultFeatureFlagValue, FeatureFlag } from "../../../enums/feature-flag.enum";
+import { ServerConfig } from "../../../platform/abstractions/config/server-config";
 
 import { EncryptServiceImplementation } from "./encrypt.service.implementation";
 
@@ -26,17 +28,65 @@ describe("EncryptService", () => {
     encryptService = new EncryptServiceImplementation(cryptoFunctionService, logService, true);
   });
 
+  describe("onServerConfigChange", () => {
+    const newConfig = mock<ServerConfig>();
+
+    afterEach(() => {
+      jest.resetAllMocks();
+    });
+
+    it("updates internal flag with default value when not present in config", () => {
+      encryptService.onServerConfigChange(newConfig);
+
+      expect((encryptService as any).blockType0).toBe(
+        DefaultFeatureFlagValue[FeatureFlag.PM17987_BlockType0],
+      );
+    });
+
+    test.each([true, false])("updates internal flag with value in config", (expectedValue) => {
+      newConfig.featureStates = { [FeatureFlag.PM17987_BlockType0]: expectedValue };
+
+      encryptService.onServerConfigChange(newConfig);
+
+      expect((encryptService as any).blockType0).toBe(expectedValue);
+    });
+  });
+
   describe("encrypt", () => {
     it("throws if no key is provided", () => {
       return expect(encryptService.encrypt(null, null)).rejects.toThrow(
         "No encryption key provided.",
       );
     });
-    it("returns null if no data is provided", async () => {
-      const key = mock<SymmetricCryptoKey>();
+
+    it("throws if type 0 key is provided with flag turned on", async () => {
+      (encryptService as any).blockType0 = true;
+      const key = new SymmetricCryptoKey(makeStaticByteArray(32));
+      const mock32Key = mock<SymmetricCryptoKey>();
+      mock32Key.key = makeStaticByteArray(32);
+
+      await expect(encryptService.encrypt(null!, key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+      await expect(encryptService.encrypt(null!, mock32Key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+
+      const plainValue = "data";
+      await expect(encryptService.encrypt(plainValue, key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+      await expect(encryptService.encrypt(plainValue, mock32Key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+    });
+
+    it("returns null if no data is provided with valid key", async () => {
+      const key = new SymmetricCryptoKey(makeStaticByteArray(64));
       const actual = await encryptService.encrypt(null, key);
       expect(actual).toBeNull();
     });
+
     it("creates an EncString for Aes256Cbc", async () => {
       const key = new SymmetricCryptoKey(makeStaticByteArray(32));
       const plainValue = "data";
@@ -53,6 +103,7 @@ describe("EncryptService", () => {
       expect(Utils.fromB64ToArray(result.data).length).toEqual(4);
       expect(Utils.fromB64ToArray(result.iv).length).toEqual(16);
     });
+
     it("creates an EncString for Aes256Cbc_HmacSha256_B64", async () => {
       const key = new SymmetricCryptoKey(makeStaticByteArray(64));
       const plainValue = "data";
@@ -90,6 +141,21 @@ describe("EncryptService", () => {
       );
     });
 
+    it("throws if type 0 key provided with flag turned on", async () => {
+      (encryptService as any).blockType0 = true;
+      const key = new SymmetricCryptoKey(makeStaticByteArray(32));
+      const mock32Key = mock<SymmetricCryptoKey>();
+      mock32Key.key = makeStaticByteArray(32);
+
+      await expect(encryptService.encryptToBytes(plainValue, key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+
+      await expect(encryptService.encryptToBytes(plainValue, mock32Key)).rejects.toThrow(
+        "Type 0 encryption is not supported.",
+      );
+    });
+
     it("encrypts data with provided Aes256Cbc key and returns correct encbuffer", async () => {
       const key = new SymmetricCryptoKey(makeStaticByteArray(32, 0));
       const iv = makeStaticByteArray(16, 80);