crypto: add support for anti-forensic split algorithm

The LUKS format specifies an anti-forensic split algorithm which
is used to artificially expand the size of the key material on
disk. This is an implementation of that algorithm.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

crypto/afsplit.c

@@ -0,0 +1,158 @@
+/*
+ * QEMU Crypto anti forensic information splitter
+ *
+ * Copyright (c) 2015-2016 Red Hat, Inc.
+ *
+ * Derived from cryptsetup package lib/luks1/af.c
+ *
+ * Copyright (C) 2004, Clemens Fruhwirth <clemens@endorphin.org>
+ * Copyright (C) 2009-2012, Red Hat, Inc. All rights reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "crypto/afsplit.h"
+#include "crypto/random.h"
+
+
+static void qcrypto_afsplit_xor(size_t blocklen,
+                                const uint8_t *in1,
+                                const uint8_t *in2,
+                                uint8_t *out)
+{
+    size_t i;
+    for (i = 0; i < blocklen; i++) {
+        out[i] = in1[i] ^ in2[i];
+    }
+}
+
+
+static int qcrypto_afsplit_hash(QCryptoHashAlgorithm hash,
+                                size_t blocklen,
+                                uint8_t *block,
+                                Error **errp)
+{
+    size_t digestlen = qcrypto_hash_digest_len(hash);
+
+    size_t hashcount = blocklen / digestlen;
+    size_t finallen = blocklen % digestlen;
+    uint32_t i;
+
+    if (finallen) {
+        hashcount++;
+    } else {
+        finallen = digestlen;
+    }
+
+    for (i = 0; i < hashcount; i++) {
+        uint8_t *out = NULL;
+        size_t outlen = 0;
+        uint32_t iv = cpu_to_be32(i);
+        struct iovec in[] = {
+            { .iov_base = &iv,
+              .iov_len = sizeof(iv) },
+            { .iov_base = block + (i * digestlen),
+              .iov_len = (i == (hashcount - 1)) ? finallen : digestlen },
+        };
+
+        if (qcrypto_hash_bytesv(hash,
+                                in,
+                                G_N_ELEMENTS(in),
+                                &out, &outlen,
+                                errp) < 0) {
+            return -1;
+        }
+
+        assert(outlen == digestlen);
+        memcpy(block + (i * digestlen), out,
+               (i == (hashcount - 1)) ? finallen : digestlen);
+        g_free(out);
+    }
+
+    return 0;
+}
+
+
+int qcrypto_afsplit_encode(QCryptoHashAlgorithm hash,
+                           size_t blocklen,
+                           uint32_t stripes,
+                           const uint8_t *in,
+                           uint8_t *out,
+                           Error **errp)
+{
+    uint8_t *block = g_new0(uint8_t, blocklen);
+    size_t i;
+    int ret = -1;
+
+    for (i = 0; i < (stripes - 1); i++) {
+        if (qcrypto_random_bytes(out + (i * blocklen), blocklen, errp) < 0) {
+            goto cleanup;
+        }
+
+        qcrypto_afsplit_xor(blocklen,
+                            out + (i * blocklen),
+                            block,
+                            block);
+        if (qcrypto_afsplit_hash(hash, blocklen, block,
+                                 errp) < 0) {
+            goto cleanup;
+        }
+    }
+    qcrypto_afsplit_xor(blocklen,
+                        in,
+                        block,
+                        out + (i * blocklen));
+    ret = 0;
+
+ cleanup:
+    g_free(block);
+    return ret;
+}
+
+
+int qcrypto_afsplit_decode(QCryptoHashAlgorithm hash,
+                           size_t blocklen,
+                           uint32_t stripes,
+                           const uint8_t *in,
+                           uint8_t *out,
+                           Error **errp)
+{
+    uint8_t *block = g_new0(uint8_t, blocklen);
+    size_t i;
+    int ret = -1;
+
+    for (i = 0; i < (stripes - 1); i++) {
+        qcrypto_afsplit_xor(blocklen,
+                            in + (i * blocklen),
+                            block,
+                            block);
+        if (qcrypto_afsplit_hash(hash, blocklen, block,
+                                 errp) < 0) {
+            goto cleanup;
+        }
+    }
+
+    qcrypto_afsplit_xor(blocklen,
+                        in + (i * blocklen),
+                        block,
+                        out);
+
+    ret = 0;
+
+ cleanup:
+    g_free(block);
+    return ret;
+}