From patchwork Mon Jan 22 00:19:16 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Biggers X-Patchwork-Id: 13524715 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 155B1C47422 for ; Mon, 22 Jan 2024 00:23:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=FlwrDsxUu2h7WUCIiw/OVXoF7Te8Abg9IOeOIrg+Wz0=; b=y248IxYWC5+0IE 2nQKeOQ4G1v1I+6198Dn1jL6pPK0dTu9jjWHzIMfJRDFc4noEFV2pG9ne51p+FUB2G5PslWbujFwK /rcSXeNhfLDGiesmv6pybKs8kcwsU6KPTRV68Q9q9TRTffQIAzu0824FPAWZheK78Ht/y/AXahfCJ OzUD4zNsOlglGwb2E3qFiEsZvM7wODh1YvWxQZiTR5vnxgLWJe9zFCZlEgFPSxXZAqrqkGTHemthC uIgC7Wy/Et5u5Nfan83xacVc0qIdLK5s6GQqu/RjwK7hdMLc9SGqqVB5DQoE/e/RL/JxbrcUuoR3m 9sOrD4jAFeZzf0lqp6MA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rRi6E-00AG2j-0V; Mon, 22 Jan 2024 00:23:38 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rRi67-00AFxM-2c for linux-riscv@lists.infradead.org; Mon, 22 Jan 2024 00:23:36 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 3A64B61007; Mon, 22 Jan 2024 00:23:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87638C43394; Mon, 22 Jan 2024 00:23:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1705882981; bh=A4Q6dU0W0wB5xtZm1bf80ruC0X86VEjB52RlElp15SY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=r+NDonKz6NhhCID8CiUBaqWXBpIAB7PeZBjQrb6l7ozO5cGLv5R1QluEgDKT3y6ga XxWuO8sWDaLmQNFgjhGO4dsB97q4ZqUzWdUWRtHbcH/xOOj7fW2gihi2qWbb9oPcgD qFLUE491oSvqt37SH1/ldqx10hHmxWqvfGFh3apj3B72zJicqtbyR8/J3FWIwzCXV1 YG4WDbdDVYE9JaAayiRMn8IQo33AzYP1p1mHrbMVF+LF6HmZvfEtSukyS/TGMPjPLk 5G8d1diKZMcszQ1JxkWCr+OzgHjOfyiVzGNX1fir1rf0WXc1GkrQ8xlKeNVCkdnkXd hZkbteEhT5z7w== From: Eric Biggers To: linux-crypto@vger.kernel.org, linux-riscv@lists.infradead.org Cc: linux-kernel@vger.kernel.org, Albert Ou , Andy Chiu , Ard Biesheuvel , =?utf-8?q?Christoph_M=C3=BCllner?= , Heiko Stuebner , Jerry Shih , Palmer Dabbelt , Paul Walmsley , Phoebe Chen , hongrong.hsu@sifive.com Subject: [PATCH v3 05/10] crypto: riscv - add vector crypto accelerated ChaCha20 Date: Sun, 21 Jan 2024 16:19:16 -0800 Message-ID: <20240122002024.27477-6-ebiggers@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240122002024.27477-1-ebiggers@kernel.org> References: <20240122002024.27477-1-ebiggers@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240121_162331_966615_5D0D9094 X-CRM114-Status: GOOD ( 28.29 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org From: Jerry Shih Add an implementation of ChaCha20 using the Zvkb extension. The assembly code is derived from OpenSSL code (openssl/openssl#21923) that was dual-licensed so that it could be reused in the kernel. Nevertheless, the assembly has been significantly reworked for integration with the kernel, for example by using a regular .S file instead of the so-called perlasm, using the assembler instead of bare '.inst', and reducing code duplication. Signed-off-by: Jerry Shih Co-developed-by: Eric Biggers Signed-off-by: Eric Biggers --- arch/riscv/crypto/Kconfig | 11 + arch/riscv/crypto/Makefile | 3 + arch/riscv/crypto/chacha-riscv64-glue.c | 101 ++++++++ arch/riscv/crypto/chacha-riscv64-zvkb.S | 294 ++++++++++++++++++++++++ 4 files changed, 409 insertions(+) create mode 100644 arch/riscv/crypto/chacha-riscv64-glue.c create mode 100644 arch/riscv/crypto/chacha-riscv64-zvkb.S diff --git a/arch/riscv/crypto/Kconfig b/arch/riscv/crypto/Kconfig index ebe805fa3f5f7..cb59e1d954952 100644 --- a/arch/riscv/crypto/Kconfig +++ b/arch/riscv/crypto/Kconfig @@ -11,11 +11,22 @@ config CRYPTO_AES_RISCV64 help Block cipher: AES cipher algorithms Length-preserving ciphers: AES with ECB, CBC, CTR, XTS Architecture: riscv64 using: - Zvkned vector crypto extension - Zvbb vector extension (XTS) - Zvkb vector crypto extension (CTR) - Zvkg vector crypto extension (XTS) +config CRYPTO_CHACHA_RISCV64 + tristate "Ciphers: ChaCha" + depends on 64BIT && RISCV_ISA_V && TOOLCHAIN_HAS_VECTOR_CRYPTO + select CRYPTO_SKCIPHER + select CRYPTO_LIB_CHACHA_GENERIC + help + Length-preserving ciphers: ChaCha20 stream cipher algorithm + + Architecture: riscv64 using: + - Zvkb vector crypto extension + endmenu diff --git a/arch/riscv/crypto/Makefile b/arch/riscv/crypto/Makefile index 44922df7d182f..ee994c8e65509 100644 --- a/arch/riscv/crypto/Makefile +++ b/arch/riscv/crypto/Makefile @@ -1,5 +1,8 @@ # SPDX-License-Identifier: GPL-2.0-only obj-$(CONFIG_CRYPTO_AES_RISCV64) += aes-riscv64.o aes-riscv64-y := aes-riscv64-glue.o aes-riscv64-zvkned.o \ aes-riscv64-zvkned-zvbb-zvkg.o aes-riscv64-zvkned-zvkb.o + +obj-$(CONFIG_CRYPTO_CHACHA_RISCV64) += chacha-riscv64.o +chacha-riscv64-y := chacha-riscv64-glue.o chacha-riscv64-zvkb.o diff --git a/arch/riscv/crypto/chacha-riscv64-glue.c b/arch/riscv/crypto/chacha-riscv64-glue.c new file mode 100644 index 0000000000000..10b46f36375af --- /dev/null +++ b/arch/riscv/crypto/chacha-riscv64-glue.c @@ -0,0 +1,101 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * ChaCha20 using the RISC-V vector crypto extensions + * + * Copyright (C) 2023 SiFive, Inc. + * Author: Jerry Shih + */ + +#include +#include +#include +#include +#include +#include + +asmlinkage void chacha20_zvkb(const u32 key[8], const u8 *in, u8 *out, + size_t len, const u32 iv[4]); + +static int riscv64_chacha20_crypt(struct skcipher_request *req) +{ + u32 iv[CHACHA_IV_SIZE / sizeof(u32)]; + u8 block_buffer[CHACHA_BLOCK_SIZE]; + struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req); + const struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm); + struct skcipher_walk walk; + unsigned int nbytes; + unsigned int tail_bytes; + int err; + + iv[0] = get_unaligned_le32(req->iv); + iv[1] = get_unaligned_le32(req->iv + 4); + iv[2] = get_unaligned_le32(req->iv + 8); + iv[3] = get_unaligned_le32(req->iv + 12); + + err = skcipher_walk_virt(&walk, req, false); + while (walk.nbytes) { + nbytes = walk.nbytes & ~(CHACHA_BLOCK_SIZE - 1); + tail_bytes = walk.nbytes & (CHACHA_BLOCK_SIZE - 1); + kernel_vector_begin(); + if (nbytes) { + chacha20_zvkb(ctx->key, walk.src.virt.addr, + walk.dst.virt.addr, nbytes, iv); + iv[0] += nbytes / CHACHA_BLOCK_SIZE; + } + if (walk.nbytes == walk.total && tail_bytes > 0) { + memcpy(block_buffer, walk.src.virt.addr + nbytes, + tail_bytes); + chacha20_zvkb(ctx->key, block_buffer, block_buffer, + CHACHA_BLOCK_SIZE, iv); + memcpy(walk.dst.virt.addr + nbytes, block_buffer, + tail_bytes); + tail_bytes = 0; + } + kernel_vector_end(); + + err = skcipher_walk_done(&walk, tail_bytes); + } + + return err; +} + +static struct skcipher_alg riscv64_chacha_alg = { + .setkey = chacha20_setkey, + .encrypt = riscv64_chacha20_crypt, + .decrypt = riscv64_chacha20_crypt, + .min_keysize = CHACHA_KEY_SIZE, + .max_keysize = CHACHA_KEY_SIZE, + .ivsize = CHACHA_IV_SIZE, + .chunksize = CHACHA_BLOCK_SIZE, + .walksize = 4 * CHACHA_BLOCK_SIZE, + .base = { + .cra_blocksize = 1, + .cra_ctxsize = sizeof(struct chacha_ctx), + .cra_priority = 300, + .cra_name = "chacha20", + .cra_driver_name = "chacha20-riscv64-zvkb", + .cra_module = THIS_MODULE, + }, +}; + +static int __init riscv64_chacha_mod_init(void) +{ + if (riscv_isa_extension_available(NULL, ZVKB) && + riscv_vector_vlen() >= 128) + return crypto_register_skcipher(&riscv64_chacha_alg); + + return -ENODEV; +} + +static void __exit riscv64_chacha_mod_exit(void) +{ + crypto_unregister_skcipher(&riscv64_chacha_alg); +} + +module_init(riscv64_chacha_mod_init); +module_exit(riscv64_chacha_mod_exit); + +MODULE_DESCRIPTION("ChaCha20 (RISC-V accelerated)"); +MODULE_AUTHOR("Jerry Shih "); +MODULE_LICENSE("GPL"); +MODULE_ALIAS_CRYPTO("chacha20"); diff --git a/arch/riscv/crypto/chacha-riscv64-zvkb.S b/arch/riscv/crypto/chacha-riscv64-zvkb.S new file mode 100644 index 0000000000000..bf057737ac693 --- /dev/null +++ b/arch/riscv/crypto/chacha-riscv64-zvkb.S @@ -0,0 +1,294 @@ +/* SPDX-License-Identifier: Apache-2.0 OR BSD-2-Clause */ +// +// This file is dual-licensed, meaning that you can use it under your +// choice of either of the following two licenses: +// +// Copyright 2023 The OpenSSL Project Authors. All Rights Reserved. +// +// Licensed under the Apache License 2.0 (the "License"). You can obtain +// a copy in the file LICENSE in the source distribution or at +// https://www.openssl.org/source/license.html +// +// or +// +// Copyright (c) 2023, Jerry Shih +// Copyright 2024 Google LLC +// All rights reserved. +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions +// are met: +// 1. Redistributions of source code must retain the above copyright +// notice, this list of conditions and the following disclaimer. +// 2. Redistributions in binary form must reproduce the above copyright +// notice, this list of conditions and the following disclaimer in the +// documentation and/or other materials provided with the distribution. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +// The generated code of this file depends on the following RISC-V extensions: +// - RV64I +// - RISC-V Vector ('V') with VLEN >= 128 +// - RISC-V Vector Cryptography Bit-manipulation extension ('Zvkb') + +#include + +.text +.option arch, +zvkb + +#define KEYP a0 +#define INP a1 +#define OUTP a2 +#define LEN a3 +#define IVP a4 + +#define CONSTS0 a5 +#define CONSTS1 a6 +#define CONSTS2 a7 +#define CONSTS3 t0 +#define TMP t1 +#define VL t2 +#define STRIDE t3 +#define NROUNDS t4 +#define KEY0 s0 +#define KEY1 s1 +#define KEY2 s2 +#define KEY3 s3 +#define KEY4 s4 +#define KEY5 s5 +#define KEY6 s6 +#define KEY7 s7 +#define COUNTER s8 +#define NONCE0 s9 +#define NONCE1 s10 +#define NONCE2 s11 + +.macro chacha_round a0, b0, c0, d0, a1, b1, c1, d1, \ + a2, b2, c2, d2, a3, b3, c3, d3 + // a += b; d ^= a; d = rol(d, 16); + vadd.vv \a0, \a0, \b0 + vadd.vv \a1, \a1, \b1 + vadd.vv \a2, \a2, \b2 + vadd.vv \a3, \a3, \b3 + vxor.vv \d0, \d0, \a0 + vxor.vv \d1, \d1, \a1 + vxor.vv \d2, \d2, \a2 + vxor.vv \d3, \d3, \a3 + vror.vi \d0, \d0, 32 - 16 + vror.vi \d1, \d1, 32 - 16 + vror.vi \d2, \d2, 32 - 16 + vror.vi \d3, \d3, 32 - 16 + + // c += d; b ^= c; b = rol(b, 12); + vadd.vv \c0, \c0, \d0 + vadd.vv \c1, \c1, \d1 + vadd.vv \c2, \c2, \d2 + vadd.vv \c3, \c3, \d3 + vxor.vv \b0, \b0, \c0 + vxor.vv \b1, \b1, \c1 + vxor.vv \b2, \b2, \c2 + vxor.vv \b3, \b3, \c3 + vror.vi \b0, \b0, 32 - 12 + vror.vi \b1, \b1, 32 - 12 + vror.vi \b2, \b2, 32 - 12 + vror.vi \b3, \b3, 32 - 12 + + // a += b; d ^= a; d = rol(d, 8); + vadd.vv \a0, \a0, \b0 + vadd.vv \a1, \a1, \b1 + vadd.vv \a2, \a2, \b2 + vadd.vv \a3, \a3, \b3 + vxor.vv \d0, \d0, \a0 + vxor.vv \d1, \d1, \a1 + vxor.vv \d2, \d2, \a2 + vxor.vv \d3, \d3, \a3 + vror.vi \d0, \d0, 32 - 8 + vror.vi \d1, \d1, 32 - 8 + vror.vi \d2, \d2, 32 - 8 + vror.vi \d3, \d3, 32 - 8 + + // c += d; b ^= c; b = rol(b, 7); + vadd.vv \c0, \c0, \d0 + vadd.vv \c1, \c1, \d1 + vadd.vv \c2, \c2, \d2 + vadd.vv \c3, \c3, \d3 + vxor.vv \b0, \b0, \c0 + vxor.vv \b1, \b1, \c1 + vxor.vv \b2, \b2, \c2 + vxor.vv \b3, \b3, \c3 + vror.vi \b0, \b0, 32 - 7 + vror.vi \b1, \b1, 32 - 7 + vror.vi \b2, \b2, 32 - 7 + vror.vi \b3, \b3, 32 - 7 +.endm + +// void chacha20_zvkb(const u32 key[8], const u8 *in, u8 *out, size_t len, +// const u32 iv[4]); +// +// |len| must be nonzero and a multiple of 64 (CHACHA_BLOCK_SIZE). +// The counter is treated as 32-bit, following the RFC7539 convention. +SYM_FUNC_START(chacha20_zvkb) + srli LEN, LEN, 6 // Bytes to blocks + + addi sp, sp, -96 + sd s0, 0(sp) + sd s1, 8(sp) + sd s2, 16(sp) + sd s3, 24(sp) + sd s4, 32(sp) + sd s5, 40(sp) + sd s6, 48(sp) + sd s7, 56(sp) + sd s8, 64(sp) + sd s9, 72(sp) + sd s10, 80(sp) + sd s11, 88(sp) + + li STRIDE, 64 + + // Set up the initial state matrix in scalar registers. + li CONSTS0, 0x61707865 // "expa" little endian + li CONSTS1, 0x3320646e // "nd 3" little endian + li CONSTS2, 0x79622d32 // "2-by" little endian + li CONSTS3, 0x6b206574 // "te k" little endian + lw KEY0, 0(KEYP) + lw KEY1, 4(KEYP) + lw KEY2, 8(KEYP) + lw KEY3, 12(KEYP) + lw KEY4, 16(KEYP) + lw KEY5, 20(KEYP) + lw KEY6, 24(KEYP) + lw KEY7, 28(KEYP) + lw COUNTER, 0(IVP) + lw NONCE0, 4(IVP) + lw NONCE1, 8(IVP) + lw NONCE2, 12(IVP) + +.Lblock_loop: + // Set vl to the number of blocks to process in this iteration. + vsetvli VL, LEN, e32, m1, ta, ma + + // Set up the initial state matrix for the next VL blocks in v0-v15. + // v{i} holds the i'th 32-bit word of the state matrix for all blocks. + // Note that only the counter word, at index 12, differs across blocks. + vmv.v.x v0, CONSTS0 + vmv.v.x v1, CONSTS1 + vmv.v.x v2, CONSTS2 + vmv.v.x v3, CONSTS3 + vmv.v.x v4, KEY0 + vmv.v.x v5, KEY1 + vmv.v.x v6, KEY2 + vmv.v.x v7, KEY3 + vmv.v.x v8, KEY4 + vmv.v.x v9, KEY5 + vmv.v.x v10, KEY6 + vmv.v.x v11, KEY7 + vid.v v12 + vadd.vx v12, v12, COUNTER + vmv.v.x v13, NONCE0 + vmv.v.x v14, NONCE1 + vmv.v.x v15, NONCE2 + + // Load the first half of the input data for each block into v16-v23. + // v{16+i} holds the i'th 32-bit word for all blocks. + vlsseg8e32.v v16, (INP), STRIDE + + li NROUNDS, 20 +.Lnext_doubleround: + addi NROUNDS, NROUNDS, -2 + // column round + chacha_round v0, v4, v8, v12, v1, v5, v9, v13, \ + v2, v6, v10, v14, v3, v7, v11, v15 + // diagonal round + chacha_round v0, v5, v10, v15, v1, v6, v11, v12, \ + v2, v7, v8, v13, v3, v4, v9, v14 + bnez NROUNDS, .Lnext_doubleround + + // Load the second half of the input data for each block into v24-v31. + // v{24+i} holds the {8+i}'th 32-bit word for all blocks. + addi TMP, INP, 32 + vlsseg8e32.v v24, (TMP), STRIDE + + // Finalize the first half of the keystream for each block. + vadd.vx v0, v0, CONSTS0 + vadd.vx v1, v1, CONSTS1 + vadd.vx v2, v2, CONSTS2 + vadd.vx v3, v3, CONSTS3 + vadd.vx v4, v4, KEY0 + vadd.vx v5, v5, KEY1 + vadd.vx v6, v6, KEY2 + vadd.vx v7, v7, KEY3 + + // Encrypt/decrypt the first half of the data for each block. + vxor.vv v16, v16, v0 + vxor.vv v17, v17, v1 + vxor.vv v18, v18, v2 + vxor.vv v19, v19, v3 + vxor.vv v20, v20, v4 + vxor.vv v21, v21, v5 + vxor.vv v22, v22, v6 + vxor.vv v23, v23, v7 + + // Store the first half of the output data for each block. + vssseg8e32.v v16, (OUTP), STRIDE + + // Finalize the second half of the keystream for each block. + vadd.vx v8, v8, KEY4 + vadd.vx v9, v9, KEY5 + vadd.vx v10, v10, KEY6 + vadd.vx v11, v11, KEY7 + vid.v v0 + vadd.vx v12, v12, COUNTER + vadd.vx v13, v13, NONCE0 + vadd.vx v14, v14, NONCE1 + vadd.vx v15, v15, NONCE2 + vadd.vv v12, v12, v0 + + // Encrypt/decrypt the second half of the data for each block. + vxor.vv v24, v24, v8 + vxor.vv v25, v25, v9 + vxor.vv v26, v26, v10 + vxor.vv v27, v27, v11 + vxor.vv v29, v29, v13 + vxor.vv v28, v28, v12 + vxor.vv v30, v30, v14 + vxor.vv v31, v31, v15 + + // Store the second half of the output data for each block. + addi TMP, OUTP, 32 + vssseg8e32.v v24, (TMP), STRIDE + + // Update the counter, the remaining number of blocks, and the input and + // output pointers according to the number of blocks processed (VL). + add COUNTER, COUNTER, VL + sub LEN, LEN, VL + slli TMP, VL, 6 + add OUTP, OUTP, TMP + add INP, INP, TMP + bnez LEN, .Lblock_loop + + ld s0, 0(sp) + ld s1, 8(sp) + ld s2, 16(sp) + ld s3, 24(sp) + ld s4, 32(sp) + ld s5, 40(sp) + ld s6, 48(sp) + ld s7, 56(sp) + ld s8, 64(sp) + ld s9, 72(sp) + ld s10, 80(sp) + ld s11, 88(sp) + addi sp, sp, 96 + ret +SYM_FUNC_END(chacha20_zvkb)