diff --git a/docs/components/rmm-el3-comms-spec.rst b/docs/components/rmm-el3-comms-spec.rst
index f1ca031..dfdabc6 100644
--- a/docs/components/rmm-el3-comms-spec.rst
+++ b/docs/components/rmm-el3-comms-spec.rst
@@ -52,8 +52,8 @@
   - ``RES0``: Bit 31 of the version number is reserved 0 as to maintain
     consistency with the versioning schemes used in other parts of RMM.
 
-This document specifies the 0.4 version of Boot Interface ABI and RMM-EL3
-services specification and the 0.4 version of the Boot Manifest.
+This document specifies the 0.5 version of Boot Interface ABI and RMM-EL3
+services specification and the 0.5 version of the Boot Manifest.
 
 .. _rmm_el3_boot_interface:
 
@@ -671,6 +671,54 @@
    ``E_RMM_OK``,No errors detected
 
 
+RMM_MECID_KEY_UPDATE command
+============================
+
+This command updates the tweak for the encryption key/programs a new encryption key
+associated with a given MECID. After the execution of this command, all memory
+accesses associated with the MECID are encrypted/decrypted using the new key.
+This command is available from v0.5 of the RMM-EL3 interface.
+
+FID
+---
+
+``0xC40001B6``
+
+Input values
+------------
+
+.. csv-table:: Input values for RMM_MECID_KEY_UPDATE
+   :header: "Name", "Register", "Field", "Type", "Description"
+   :widths: 1 1 1 1 5
+
+   fid,x0,[63:0],UInt64,Command FID
+   mecid,x1,[15:0],UInt64,"mecid is a 16-bit value between 0 and 65,535 that identifies the MECID for which the encryption key is to be updated. Value has to be a valid MECID as per field MECIDWidthm1 read from MECIDR_EL2. Bits [63:16] must be 0."
+
+Output values
+-------------
+
+.. csv-table:: Output values for RMM_MECID_KEY_UPDATE
+   :header: "Name", "Register", "Field", "Type", "Description"
+   :widths: 1 1 1 1 5
+
+   Result,x0,[63:0],Error Code,Command return status. Valid for all opcodes listed in input values
+
+
+Failure conditions
+------------------
+
+The table below shows all the possible error codes returned in ``Result`` upon
+a failure. The errors are ordered by condition check.
+
+.. csv-table:: Failure conditions for RMM_MECID_KEY_UPDATE
+   :header: "ID", "Condition"
+   :widths: 1 5
+
+   ``E_RMM_INVAL``,"if mecid is invalid (larger than 65,535 or than the maximum MECID width, determined by MECIDR_EL2.MECIDWidthm1)"
+   ``E_RMM_UNK``,"An unknown error occurred whilst processing the command or the SMC is not present if interface version is <0.5"
+   ``E_RMM_OK``,No errors detected
+
+
 RMM-EL3 world switch register save restore convention
 _____________________________________________________
 
diff --git a/docs/porting-guide.rst b/docs/porting-guide.rst
index 0f0dedd..327c67b 100644
--- a/docs/porting-guide.rst
+++ b/docs/porting-guide.rst
@@ -2350,6 +2350,24 @@
 
 When ENABLE_RME is disabled, this function is not used.
 
+Function : plat_rmm_mecid_key_update() [when ENABLE_RME == 1]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : uint16_t
+    Return   : int
+
+This function is invoked by BL31's RMMD when there is a request from the RMM
+monitor to update the tweak for the encryption key associated to a MECID.
+
+The first parameter (``uint16_t mecid``) contains the MECID for which the
+encryption key is to be updated.
+
+Return value is 0 upon success and -EFAULT otherwise.
+
+This function needs to be implemented by a platform if it enables RME.
+
 Function : plat_rmmd_el3_token_sign_push_req() [mandatory when RMMD_ENABLE_EL3_TOKEN_SIGN == 1]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/include/arch/aarch64/arch.h b/include/arch/aarch64/arch.h
index 627416f..67fdead 100644
--- a/include/arch/aarch64/arch.h
+++ b/include/arch/aarch64/arch.h
@@ -1585,4 +1585,11 @@
 #define CLUSTERPMCR_N_SHIFT		U(11)
 #define CLUSTERPMCR_N_MASK		U(0x1f)
 
+/*******************************************************************************
+ * FEAT_MEC - Memory Encryption Contexts
+ ******************************************************************************/
+#define MECIDR_EL2			S3_4_C10_C8_7
+#define MECIDR_EL2_MECIDWidthm1_MASK	U(0xf)
+#define MECIDR_EL2_MECIDWidthm1_SHIFT	U(0)
+
 #endif /* ARCH_H */
diff --git a/include/arch/aarch64/arch_helpers.h b/include/arch/aarch64/arch_helpers.h
index f85da97..55b6199 100644
--- a/include/arch/aarch64/arch_helpers.h
+++ b/include/arch/aarch64/arch_helpers.h
@@ -746,6 +746,9 @@
 
 DEFINE_RENAME_SYSREG_RW_FUNCS(fpmr, FPMR)
 
+/* FEAT_MEC Registers */
+DEFINE_RENAME_SYSREG_READ_FUNC(mecidr_el2, MECIDR_EL2)
+
 #define IS_IN_EL(x) \
 	(GET_EL(read_CurrentEl()) == MODE_EL##x)
 
diff --git a/include/plat/common/platform.h b/include/plat/common/platform.h
index b43f131..708cbcd 100644
--- a/include/plat/common/platform.h
+++ b/include/plat/common/platform.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2024, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2025, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -398,6 +398,7 @@
 int plat_rmmd_el3_token_sign_pull_resp(struct el3_token_sign_response *resp);
 size_t plat_rmmd_get_el3_rmm_shared_mem(uintptr_t *shared);
 int plat_rmmd_load_manifest(struct rmm_manifest *manifest);
+int plat_rmmd_mecid_key_update(uint16_t mecid);
 #endif
 
 /*******************************************************************************
diff --git a/include/services/rmmd_svc.h b/include/services/rmmd_svc.h
index 0cc8628..8bf9319 100644
--- a/include/services/rmmd_svc.h
+++ b/include/services/rmmd_svc.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2021-2025, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -161,6 +161,18 @@
 #define RMM_EL3_TOKEN_SIGN_PULL_RESP_OP         U(2)
 #define RMM_EL3_TOKEN_SIGN_GET_RAK_PUB_OP       U(3)
 
+/* Starting RMM-EL3 interface version 0.5 */
+
+/*
+ * Function code to support update of MEC keys.
+ * The arguments of this SMC are:
+ * 	arg0 - Function ID.
+ * 	arg1 - MECID
+ * The return arguments are:
+ * 	ret0 - Status/Error
+ */
+#define RMM_MECID_KEY_UPDATE			SMC64_RMMD_EL3_FID(U(6))
+
 /* ECC Curve types for attest key generation */
 #define ATTEST_KEY_CURVE_ECC_SECP384R1		U(0)
 
@@ -188,7 +200,7 @@
  * Increase this when a bug is fixed, or a feature is added without
  * breaking compatibility.
  */
-#define RMM_EL3_IFC_VERSION_MINOR	(U(4))
+#define RMM_EL3_IFC_VERSION_MINOR	(U(5))
 
 #define RMM_EL3_INTERFACE_VERSION				\
 	(((RMM_EL3_IFC_VERSION_MAJOR << 16) & 0x7FFFF) |	\
diff --git a/plat/arm/board/fvp/fvp_common.c b/plat/arm/board/fvp/fvp_common.c
index 7d76814..98d4bbc 100644
--- a/plat/arm/board/fvp/fvp_common.c
+++ b/plat/arm/board/fvp/fvp_common.c
@@ -7,6 +7,8 @@
 #include <assert.h>
 #include <string.h>
 
+#include <arch.h>
+#include <arch_helpers.h>
 #include <common/debug.h>
 #include <drivers/arm/cci.h>
 #include <drivers/arm/ccn.h>
@@ -775,4 +777,16 @@
 
 	return 0;
 }
+
+/*
+ * Update encryption key associated with @mecid.
+ */
+int plat_rmmd_mecid_key_update(uint16_t mecid)
+{
+	/*
+	 * FVP does not provide an interface to change the encryption key associated
+	 * with MECID. Hence always return success.
+	 */
+	return 0;
+}
 #endif	/* ENABLE_RME */
diff --git a/plat/arm/board/neoverse_rd/platform/rdv3/rdv3_common.c b/plat/arm/board/neoverse_rd/platform/rdv3/rdv3_common.c
index 364bce1..b1ee5e6 100644
--- a/plat/arm/board/neoverse_rd/platform/rdv3/rdv3_common.c
+++ b/plat/arm/board/neoverse_rd/platform/rdv3/rdv3_common.c
@@ -187,6 +187,17 @@
 	return 0;
 }
 
+/*
+ * Update encryption key associated with @mecid.
+ */
+int plat_rmmd_mecid_key_update(uint16_t mecid)
+{
+	/*
+	 * TODO
+	 */
+	return 0;
+}
+
 int plat_rse_comms_init(void)
 {
 	struct mhu_addr mhu_addresses;
diff --git a/services/std_svc/rmmd/rmmd_main.c b/services/std_svc/rmmd/rmmd_main.c
index 10a2c42..3ebae13 100644
--- a/services/std_svc/rmmd/rmmd_main.c
+++ b/services/std_svc/rmmd/rmmd_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2021-2025, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -470,6 +470,33 @@
 	return E_RMM_OK;
 }
 
+/*
+ * Update encryption key associated with @mecid.
+ */
+static int rmmd_mecid_key_update(uint64_t mecid)
+{
+	uint64_t mecid_width, mecid_width_mask;
+	int ret;
+
+	/*
+	 * Check whether the mecid parameter is at most MECIDR_EL2.MECIDWidthm1 + 1
+	 * in length.
+	 */
+	mecid_width = ((read_mecidr_el2() >> MECIDR_EL2_MECIDWidthm1_SHIFT) &
+		MECIDR_EL2_MECIDWidthm1_MASK) + 1;
+	mecid_width_mask = ((1 << mecid_width) - 1);
+	if ((mecid & ~mecid_width_mask) != 0U) {
+		return E_RMM_INVAL;
+	}
+
+	ret = plat_rmmd_mecid_key_update(mecid);
+
+	if (ret != 0) {
+		return E_RMM_UNK;
+	}
+	return E_RMM_OK;
+}
+
 /*******************************************************************************
  * This function handles RMM-EL3 interface SMCs
  ******************************************************************************/
@@ -519,6 +546,9 @@
 		VERBOSE("RMMD: running rmmd_rmm_sync_exit\n");
 		rmmd_rmm_sync_exit(x1);
 
+	case RMM_MECID_KEY_UPDATE:
+		ret = rmmd_mecid_key_update(x1);
+		SMC_RET1(handle, ret);
 	default:
 		WARN("RMMD: Unsupported RMM-EL3 call 0x%08x\n", smc_fid);
 		SMC_RET1(handle, SMC_UNK);