1 files changed, 362 insertions, 0 deletions
diff --git a/providers/implementations/ciphers/cipher_cts.c b/providers/implementations/ciphers/cipher_cts.c
new file mode 100644
index 0000000000..3e880931c1
--- /dev/null
+++ b/providers/implementations/ciphers/cipher_cts.c
@@ -0,0 +1,362 @@
+/*
+ * Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+/*
+ * Helper functions for 128 bit CBC CTS ciphers (Currently AES and Camellia).
+ *
+ * The function dispatch tables are embedded into cipher_aes.c
+ * and cipher_camellia.c using cipher_aes_cts.inc and cipher_camellia_cts.inc
+ */
+
+/*
+ * Refer to SP800-38A-Addendum
+ *
+ * Ciphertext stealing encrypts plaintext using a block cipher, without padding
+ * the message to a multiple of the block size, so the ciphertext is the same
+ * size as the plaintext.
+ * It does this by altering processing of the last two blocks of the message.
+ * The processing of all but the last two blocks is unchanged, but a portion of
+ * the second-last block's ciphertext is "stolen" to pad the last plaintext
+ * block. The padded final block is then encrypted as usual.
+ * The final ciphertext for the last two blocks, consists of the partial block
+ * (with the "stolen" portion omitted) plus the full final block,
+ * which are the same size as the original plaintext.
+ * Decryption requires decrypting the final block first, then restoring the
+ * stolen ciphertext to the partial block, which can then be decrypted as usual.
+
+ * AES_CBC_CTS has 3 variants:
+ *  (1) CS1 The NIST variant.
+ *      If the length is a multiple of the blocksize it is the same as CBC mode.
+ *      otherwise it produces C1||C2||(C(n-1))*||Cn.
+ *      Where C(n-1)* is a partial block.
+ *  (2) CS2
+ *      If the length is a multiple of the blocksize it is the same as CBC mode.
+ *      otherwise it produces C1||C2||Cn||(C(n-1))*.
+ *      Where C(n-1)* is a partial block.
+ *  (3) CS3 The Kerberos5 variant.
+ *      Produces C1||C2||Cn||(C(n-1))* regardless of the length.
+ *      If the length is a multiple of the blocksize it looks similar to CBC mode
+ *      with the last 2 blocks swapped.
+ *      Otherwise it is the same as CS2.
+ */
+
+#include "e_os.h" /* strcasecmp */
+#include <openssl/core_names.h>
+#include "prov/ciphercommon.h"
+#include "internal/nelem.h"
+#include "cipher_cts.h"
+
+/* The value assigned to 0 is the default */
+#define CTS_CS1 0
+#define CTS_CS2 1
+#define CTS_CS3 2
+
+#define CTS_BLOCK_SIZE 16
+
+typedef union {
+    size_t align;
+    unsigned char c[CTS_BLOCK_SIZE];
+} aligned_16bytes;
+
+typedef struct cts_mode_name2id_st {
+    unsigned int id;
+    const char *name;
+} CTS_MODE_NAME2ID;
+
+static CTS_MODE_NAME2ID cts_modes[] =
+{
+    { CTS_CS1, OSSL_CIPHER_CTS_MODE_CS1 },
+    { CTS_CS2, OSSL_CIPHER_CTS_MODE_CS2 },
+    { CTS_CS3, OSSL_CIPHER_CTS_MODE_CS3 },
+};
+
+const char *ossl_cipher_cbc_cts_mode_id2name(unsigned int id)
+{
+    size_t i;
+
+    for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
+        if (cts_modes[i].id == id)
+            return cts_modes[i].name;
+    }
+    return NULL;
+}
+
+int ossl_cipher_cbc_cts_mode_name2id(const char *name)
+{
+    size_t i;
+
+    for (i = 0; i < OSSL_NELEM(cts_modes); ++i) {
+        if (strcasecmp(name, cts_modes[i].name) == 0)
+            return (int)cts_modes[i].id;
+    }
+    return -1;
+}
+
+static size_t cts128_cs1_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    aligned_16bytes tmp_in;
+    size_t residue;
+
+    residue = len % CTS_BLOCK_SIZE;
+    len -= residue;
+    if (!ctx->hw->cipher(ctx, out, in, len))
+        return 0;
+
+    if (residue == 0)
+        return len;
+
+    in += len;
+    out += len;
+
+    memset(tmp_in.c, 0, sizeof(tmp_in));
+    memcpy(tmp_in.c, in, residue);
+    if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE + residue, tmp_in.c,
+                         CTS_BLOCK_SIZE))
+        return 0;
+    return len + residue;
+}
+
+static void do_xor(const unsigned char *in1, const unsigned char *in2,
+                   size_t len, unsigned char *out)
+{
+    size_t i;
+
+    for (i = 0; i < len; ++i)
+        out[i] = in1[i] ^ in2[i];
+}
+
+static size_t cts128_cs1_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    aligned_16bytes mid_iv, ct_mid, pt_last;
+    size_t residue;
+
+    residue = len % CTS_BLOCK_SIZE;
+    if (residue == 0) {
+        /* If there are no partial blocks then it is the same as CBC mode */
+        if (!ctx->hw->cipher(ctx, out, in, len))
+            return 0;
+        return len;
+    }
+    /* Process blocks at the start - but leave the last 2 blocks */
+    len -= CTS_BLOCK_SIZE + residue;
+    if (len > 0) {
+        if (!ctx->hw->cipher(ctx, out, in, len))
+            return 0;
+        in += len;
+        out += len;
+    }
+    /* Save the iv that will be used by the second last block */
+    memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
+
+    /* Decrypt the last block first using an iv of zero */
+    memset(ctx->iv, 0, CTS_BLOCK_SIZE);
+    if (!ctx->hw->cipher(ctx, pt_last.c, in + residue, CTS_BLOCK_SIZE))
+        return 0;
+
+    /*
+     * Rebuild the ciphertext of the second last block as a combination of
+     * the decrypted last block + replace the start with the ciphertext bytes
+     * of the partial second last block.
+     */
+    memcpy(ct_mid.c, in, residue);
+    memcpy(ct_mid.c + residue, pt_last.c + residue, CTS_BLOCK_SIZE - residue);
+    /*
+     * Restore the last partial ciphertext block.
+     * Now that we have the cipher text of the second last block, apply
+     * that to the partial plaintext end block. We have already decrypted the
+     * block using an IV of zero. For decryption the IV is just XORed after
+     * doing an Cipher CBC block - so just XOR in the cipher text.
+     */
+    do_xor(ct_mid.c, pt_last.c, residue, out + CTS_BLOCK_SIZE);
+
+    /* Restore the iv needed by the second last block */
+    memcpy(ctx->iv, mid_iv.c, CTS_BLOCK_SIZE);
+    /*
+     * Decrypt the second last plaintext block now that we have rebuilt the
+     * ciphertext.
+     */
+    if (!ctx->hw->cipher(ctx, out, ct_mid.c, CTS_BLOCK_SIZE))
+        return 0;
+
+    return len + CTS_BLOCK_SIZE + residue;
+}
+
+static size_t cts128_cs3_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    aligned_16bytes tmp_in;
+    size_t residue;
+
+    if (len <= CTS_BLOCK_SIZE)  /* CS3 requires 2 blocks */
+        return 0;
+
+    residue = len % CTS_BLOCK_SIZE;
+    if (residue == 0)
+        residue = CTS_BLOCK_SIZE;
+    len -= residue;
+
+    if (!ctx->hw->cipher(ctx, out, in, len))
+        return 0;
+
+    in += len;
+    out += len;
+
+    memset(tmp_in.c, 0, sizeof(tmp_in));
+    memcpy(tmp_in.c, in, residue);
+    memcpy(out, out - CTS_BLOCK_SIZE, residue);
+    if (!ctx->hw->cipher(ctx, out - CTS_BLOCK_SIZE, tmp_in.c, CTS_BLOCK_SIZE))
+        return 0;
+    return len + residue;
+}
+
+/*
+ * Note:
+ *  The cipher text (in) is of the form C(0), C(1), ., C(n), C(n-1)* where
+ *  C(n) is a full block and C(n-1)* can be a partial block
+ *  (but could be a full block).
+ *  This means that the output plaintext (out) needs to swap the plaintext of
+ *  the last two decoded ciphertext blocks.
+ */
+static size_t cts128_cs3_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    aligned_16bytes mid_iv, ct_mid, pt_last;
+    size_t residue;
+
+    if (len <= CTS_BLOCK_SIZE) /* CS3 requires 2 blocks */
+        return 0;
+
+    /* Process blocks at the start - but leave the last 2 blocks */
+    residue = len % CTS_BLOCK_SIZE;
+    if (residue == 0)
+        residue = CTS_BLOCK_SIZE;
+    len -= CTS_BLOCK_SIZE + residue;
+
+    if (len > 0) {
+        if (!ctx->hw->cipher(ctx, out, in, len))
+            return 0;
+        in += len;
+        out += len;
+    }
+    /* Save the iv that will be used by the second last block */
+    memcpy(mid_iv.c, ctx->iv, CTS_BLOCK_SIZE);
+
+    /* Decrypt the Cn block first using an iv of zero */
+    memset(ctx->iv, 0, CTS_BLOCK_SIZE);
+    if (!ctx->hw->cipher(ctx, pt_last.c, in, CTS_BLOCK_SIZE))
+        return 0;
+
+    /*
+     * Rebuild the ciphertext of C(n-1) as a combination of
+     * the decrypted C(n) block + replace the start with the ciphertext bytes
+     * of the partial last block.
+     */
+    memcpy(ct_mid.c, in + CTS_BLOCK_SIZE, residue);
+    if (residue != CTS_BLOCK_SIZE)
+        memcpy(ct_mid.c + residue, pt_last.c + residue, CTS_BLOCK_SIZE - residue);
+    /*
+     * Restore the last partial ciphertext block.
+     * Now that we have the cipher text of the second last block, apply
+     * that to the partial plaintext end block. We have already decrypted the
+     * block using an IV of zero. For decryption the IV is just XORed after
+     * doing an AES block - so just XOR in the ciphertext.
+     */
+    do_xor(ct_mid.c, pt_last.c, residue, out + CTS_BLOCK_SIZE);
+
+    /* Restore the iv needed by the second last block */
+    memcpy(ctx->iv, mid_iv.c, CTS_BLOCK_SIZE);
+    /*
+     * Decrypt the second last plaintext block now that we have rebuilt the
+     * ciphertext.
+     */
+    if (!ctx->hw->cipher(ctx, out, ct_mid.c, CTS_BLOCK_SIZE))
+        return 0;
+
+    return len + CTS_BLOCK_SIZE + residue;
+}
+
+static size_t cts128_cs2_encrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    if (len % CTS_BLOCK_SIZE == 0) {
+        /* If there are no partial blocks then it is the same as CBC mode */
+        if (!ctx->hw->cipher(ctx, out, in, len))
+            return 0;
+        return len;
+    }
+    /* For partial blocks CS2 is equivalent to CS3 */
+    return cts128_cs3_encrypt(ctx, in, out, len);
+}
+
+static size_t cts128_cs2_decrypt(PROV_CIPHER_CTX *ctx, const unsigned char *in,
+                                 unsigned char *out, size_t len)
+{
+    if (len % CTS_BLOCK_SIZE == 0) {
+        /* If there are no partial blocks then it is the same as CBC mode */
+        if (!ctx->hw->cipher(ctx, out, in, len))
+            return 0;
+        return len;
+    }
+    /* For partial blocks CS2 is equivalent to CS3 */
+    return cts128_cs3_decrypt(ctx, in, out, len);
+}
+
+int ossl_cipher_cbc_cts_block_update(void *vctx, unsigned char *out, size_t *outl,
+                                     size_t outsize, const unsigned char *in,
+                                     size_t inl)
+{
+    PROV_CIPHER_CTX *ctx = (PROV_CIPHER_CTX *)vctx;
+    size_t sz = 0;
+
+    if (inl < CTS_BLOCK_SIZE) /* There must be at least one block for CTS mode */
+        return 0;
+    if (outsize < inl)
+        return 0;
+    if (out == NULL) {
+        *outl = inl;
+        return 1;
+    }
+
+    /*
+     * Return an error if the update is called multiple times, only one shot
+     * is supported.
+     */
+    if (ctx->updated == 1)
+        return 0;
+
+    if (ctx->enc) {
+        if (ctx->cts_mode == CTS_CS1)
+            sz = cts128_cs1_encrypt(ctx, in, out, inl);
+        else if (ctx->cts_mode == CTS_CS2)
+            sz = cts128_cs2_encrypt(ctx, in, out, inl);
+        else if (ctx->cts_mode == CTS_CS3)
+            sz = cts128_cs3_encrypt(ctx, in, out, inl);
+    } else {
+        if (ctx->cts_mode == CTS_CS1)
+            sz = cts128_cs1_decrypt(ctx, in, out, inl);
+        else if (ctx->cts_mode == CTS_CS2)
+            sz = cts128_cs2_decrypt(ctx, in, out, inl);
+        else if (ctx->cts_mode == CTS_CS3)
+            sz = cts128_cs3_decrypt(ctx, in, out, inl);
+    }
+    if (sz == 0)
+        return 0;
+    ctx->updated = 1; /* Stop multiple updates being allowed */
+    *outl = sz;
+    return 1;
+}
+
+int ossl_cipher_cbc_cts_block_final(void *vctx, unsigned char *out, size_t *outl,
+                                    size_t outsize)
+{
+    *outl = 0;
+    return 1;
+}