1 files changed, 126 insertions, 0 deletions

diff --git a/libmincrypt/dsa_sig.c b/libmincrypt/dsa_sig.c
new file mode 100644
index 000000000..101314bd9
--- /dev/null
+++ b/libmincrypt/dsa_sig.c
@@ -0,0 +1,126 @@
+/*
+ * Copyright 2013 The Android Open Source Project
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * 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.
+ *     * Neither the name of Google Inc. nor the names of its contributors may
+ *       be used to endorse or promote products derived from this software
+ *       without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY Google Inc. ``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 Google Inc. 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.
+ */
+
+#include <string.h>
+
+#include "mincrypt/dsa_sig.h"
+#include "mincrypt/p256.h"
+
+/**
+ * Trims off the leading zero bytes and copy it to a buffer aligning it to the end.
+ */
+static inline int trim_to_p256_bytes(unsigned char dst[P256_NBYTES], unsigned char *src,
+        int src_len) {
+    int dst_offset;
+    while (*src == '\0' && src_len > 0) {
+        src++;
+        src_len--;
+    }
+    if (src_len > P256_NBYTES || src_len < 1) {
+        return 0;
+    }
+    dst_offset = P256_NBYTES - src_len;
+    memset(dst, 0, dst_offset);
+    memcpy(dst + dst_offset, src, src_len);
+    return 1;
+}
+
+/**
+ * Unpacks the ASN.1 DSA signature sequence.
+ */
+int dsa_sig_unpack(unsigned char* sig, int sig_len, p256_int* r_int, p256_int* s_int) {
+    /*
+     * Structure is:
+     *   0x30 0xNN  SEQUENCE + s_length
+     *     0x02 0xNN  INTEGER + r_length
+     *       0xAA 0xBB ..   r_length bytes of "r" (offset 4)
+     *     0x02 0xNN  INTEGER + s_length
+     *       0xMM 0xNN ..   s_length bytes of "s" (offset 6 + r_len)
+     */
+    int seq_len;
+    unsigned char r_bytes[P256_NBYTES];
+    unsigned char s_bytes[P256_NBYTES];
+    int r_len;
+    int s_len;
+
+    memset(r_bytes, 0, sizeof(r_bytes));
+    memset(s_bytes, 0, sizeof(s_bytes));
+
+    /*
+     * Must have at least:
+     * 2 bytes sequence header and length
+     * 2 bytes R integer header and length
+     * 1 byte of R
+     * 2 bytes S integer header and length
+     * 1 byte of S
+     *
+     * 8 bytes total
+     */
+    if (sig_len < 8 || sig[0] != 0x30 || sig[2] != 0x02) {
+        return 0;
+    }
+
+    seq_len = sig[1];
+    if ((seq_len <= 0) || (seq_len + 2 != sig_len)) {
+        return 0;
+    }
+
+    r_len = sig[3];
+    /*
+     * Must have at least:
+     * 2 bytes for R header and length
+     * 2 bytes S integer header and length
+     * 1 byte of S
+     */
+    if ((r_len < 1) || (r_len > seq_len - 5) || (sig[4 + r_len] != 0x02)) {
+        return 0;
+    }
+    s_len = sig[5 + r_len];
+
+    /**
+     * Must have:
+     * 2 bytes for R header and length
+     * r_len bytes for R
+     * 2 bytes S integer header and length
+     */
+    if ((s_len < 1) || (s_len != seq_len - 4 - r_len)) {
+        return 0;
+    }
+
+    /*
+     * ASN.1 encoded integers are zero-padded for positive integers. Make sure we have
+     * a correctly-sized buffer and that the resulting integer isn't too large.
+     */
+    if (!trim_to_p256_bytes(r_bytes, &sig[4], r_len)
+            || !trim_to_p256_bytes(s_bytes, &sig[6 + r_len], s_len)) {
+        return 0;
+    }
+
+    p256_from_bin(r_bytes, r_int);
+    p256_from_bin(s_bytes, s_int);
+
+    return 1;
+}