libavutil: add aes-ctr support

for supporting mp4 cenc encoding/decoding

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 129 insertions, 0 deletions

diff --git a/libavutil/aes_ctr.c b/libavutil/aes_ctr.c
new file mode 100644
index 0000000000..234354374f
--- /dev/null
+++ b/libavutil/aes_ctr.c
@@ -0,0 +1,129 @@
+/*
+ * AES-CTR cipher
+ * Copyright (c) 2015 Eran Kornblau <erankor at gmail dot com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "common.h"
+#include "aes_ctr.h"
+#include "aes.h"
+#include "random_seed.h"
+
+#define AES_BLOCK_SIZE (16)
+
+typedef struct AVAESCTR {
+    struct AVAES* aes;
+    uint8_t counter[AES_BLOCK_SIZE];
+    uint8_t encrypted_counter[AES_BLOCK_SIZE];
+    int block_offset;
+} AVAESCTR;
+
+struct AVAESCTR *av_aes_ctr_alloc(void)
+{
+    return av_mallocz(sizeof(struct AVAESCTR));
+}
+
+void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
+{
+    memcpy(a->counter, iv, AES_CTR_IV_SIZE);
+    memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
+    a->block_offset = 0;
+}
+
+const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
+{
+    return a->counter;
+}
+
+void av_aes_ctr_set_random_iv(struct AVAESCTR *a)
+{
+    uint32_t iv[2];
+
+    iv[0] = av_get_random_seed();
+    iv[1] = av_get_random_seed();
+
+    av_aes_ctr_set_iv(a, (uint8_t*)iv);
+}
+
+int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
+{
+    a->aes = av_aes_alloc();
+    if (!a->aes) {
+        return AVERROR(ENOMEM);
+    }
+
+    av_aes_init(a->aes, key, 128, 0);
+
+    memset(a->counter, 0, sizeof(a->counter));
+    a->block_offset = 0;
+
+    return 0;
+}
+
+void av_aes_ctr_free(struct AVAESCTR *a)
+{
+    if (a) {
+        av_freep(&a->aes);
+        av_freep(a);
+    }
+}
+
+static void av_aes_ctr_increment_be64(uint8_t* counter)
+{
+    uint8_t* cur_pos;
+
+    for (cur_pos = counter + 7; cur_pos >= counter; cur_pos--) {
+        (*cur_pos)++;
+        if (*cur_pos != 0) {
+            break;
+        }
+    }
+}
+
+void av_aes_ctr_increment_iv(struct AVAESCTR *a)
+{
+    av_aes_ctr_increment_be64(a->counter);
+    memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
+    a->block_offset = 0;
+}
+
+void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
+{
+    const uint8_t* src_end = src + count;
+    const uint8_t* cur_end_pos;
+    uint8_t* encrypted_counter_pos;
+
+    while (src < src_end) {
+        if (a->block_offset == 0) {
+            av_aes_crypt(a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
+
+            av_aes_ctr_increment_be64(a->counter + 8);
+        }
+
+        encrypted_counter_pos = a->encrypted_counter + a->block_offset;
+        cur_end_pos = src + AES_BLOCK_SIZE - a->block_offset;
+        cur_end_pos = FFMIN(cur_end_pos, src_end);
+
+        a->block_offset += cur_end_pos - src;
+        a->block_offset &= (AES_BLOCK_SIZE - 1);
+
+        while (src < cur_end_pos) {
+            *dst++ = *src++ ^ *encrypted_counter_pos++;
+        }
+    }
+}