common: Add base32 encoding

Base32 encoding is used to turn the RMA reset binary
challenge/response into less-typo-prone text, at 5 bits per character.

BUG=b:37952913
BRANCH=none
TEST=make runtests

Change-Id: I474750a20204ba353cea1e91982aa03e8071c0c2
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/544177
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

1 files changed, 72 insertions, 0 deletions

diff --git a/include/base32.h b/include/base32.h
new file mode 100644
index 0000000000..e519034732
--- /dev/null
+++ b/include/base32.h
@@ -0,0 +1,72 @@
+/* Copyright 2017 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Base-32 encoding/decoding, designed for manual operator entry. */
+
+#ifndef __CROS_EC_BASE32_H
+#define __CROS_EC_BASE32_H
+
+/* Symbol map for base32 encoding */
+extern const char base32_map[33];
+
+/**
+ * 5-bit CRC
+ *
+ * @param sym		New symbol to update CRC with
+ * @param previous_crc	Existing CRC value
+ * @return The updated CRC.
+ */
+uint8_t crc5_sym(int sym, uint8_t previous_crc);
+
+/**
+ * base32-encode data into a null-terminated string
+ *
+ * Uses A-Z0-9 encoding, skipping I,O,0,1 since they're easy to get mixed up.
+ *
+ * @param dest			Destination buffer; set to empty string on
+ *				error
+ * @param destlen_chars		Length of destination buffer in characters
+ * @param src			Source binary data
+ * @param srclen_bits		Length of source *in bits*.  If this is not a
+ *				multiple of 8, the *most significant* bits of
+ *				the last byte will be used.  If this is not a
+ *				multiple of 5, the least significant bits of
+ *				the last symbol will be padded with 0 bits.
+ * @param add_crc_every		If non-zero, add a CRC symbol after each group
+ *				of this many symbols.  There must be an exact
+ *				number of groups; that is, ceil(srclen_bits/5)
+ *				must be a multiple of add_crc_every.
+ * @return EC_SUCCESS, or non-zero error code.
+ */
+int base32_encode(char *dest, int destlen_chars,
+		  const void *srcbits, int srclen_bits,
+		  int add_crc_every);
+
+/**
+ * base32-decode data from a null-terminated string
+ *
+ * Ignores whitespace and '-' dashes in the source string.
+ *
+ * If the destination is smaller than the decoded bitstream, only that many
+ * bits will be decoded.  This is useful for decoding the first part of a
+ * bitstream to look for a struct version.
+ *
+ * If the destination is larger than the decoded bitstream, check the return
+ * value to determine how many bits were decoded from the source.  Note that if
+ * padding was added by base32_encode (that is, the input length was not a
+ * multiple of 5 bits), the padding will be included in the count.
+ *
+ * @param dest			Destination; must be at least
+ *				ceil(destlen_bits/8) bytes.
+ * @param destlen_bits		Length of destination *in bits*.
+ * @param src			Source string (null-terminated)
+ * @param crc_after_every	If non-zero, expect CRC symbol after every
+ *				group of this many symbols.
+ * @return Number of decoded *bits*, or -1 if error.
+ */
+int base32_decode(uint8_t *dest, int destlen_bits, const char *src,
+		  int crc_after_every);
+
+#endif