Add rudimentary support for PEM-encoding, since NSS doesn't do that.

src/lib/encoding/.may_include

@@ -1,5 +1,6 @@
 orconfig.h
 lib/cc/*.h
+lib/ctime/*.h
 lib/encoding/*.h
 lib/intmath/*.h
 lib/log/*.h

src/lib/encoding/include.am

@@ -9,6 +9,7 @@ src_lib_libtor_encoding_a_SOURCES =			\
 	src/lib/encoding/confline.c			\
 	src/lib/encoding/cstring.c			\
 	src/lib/encoding/keyval.c			\
+	src/lib/encoding/pem.c				\
 	src/lib/encoding/time_fmt.c
 
 src_lib_libtor_encoding_testing_a_SOURCES = \
@@ -21,4 +22,5 @@ noinst_HEADERS +=					\
 	src/lib/encoding/confline.h			\
 	src/lib/encoding/cstring.h			\
 	src/lib/encoding/keyval.h			\
+	src/lib/encoding/pem.h				\
 	src/lib/encoding/time_fmt.h

src/lib/encoding/pem.c

@@ -0,0 +1,106 @@
+/* Copyright (c) 2001, Matej Pfajfar.
+ * Copyright (c) 2001-2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file pem.c
+ *
+ * \brief Implement a trivial version of PEM encoding, for use with NSS.
+ *
+ * We deliberately do not support any encryption here.
+ **/
+
+#include "orconfig.h"
+
+#include "lib/encoding/pem.h"
+
+#include "lib/ctime/di_ops.h"
+#include "lib/encoding/binascii.h"
+#include "lib/log/util_bug.h"
+#include "lib/malloc/malloc.h"
+#include "lib/string/printf.h"
+#include "lib/string/util_string.h"
+
+#include <string.h>
+
+/**
+ * Return the length of a <b>src_len</b>-byte object when tagged with
+ * <b>objtype</b> and PEM-encoded.  Includes terminating NUL.
+ */
+size_t
+pem_encoded_size(size_t src_len, const char *objtype)
+{
+  return
+    strlen("-----BEGIN -----\n") +
+    strlen("-----END -----\n") +
+    strlen(objtype) * 2 +
+    base64_encode_size(src_len, BASE64_ENCODE_MULTILINE)
+    + 1;
+}
+
+/**
+ * PEM-encode the <b>srclen</b>-byte object at <b>src</b> into the
+ * <b>destlen<\b>-byte buffer at <b>dest</b>, tagging it with <b>objtype</b>.
+ * Return 0 on success and -1 on failure.
+ */
+int
+pem_encode(char *dest, size_t destlen, const uint8_t *src, size_t srclen,
+           const char *objtype)
+{
+  if (tor_snprintf(dest, destlen, "-----BEGIN %s-----\n", objtype) < 0)
+    return -1;
+
+  size_t offset = strlen(dest);
+
+  int n = base64_encode(dest + offset, destlen - offset,
+                        (const char *)src, srclen, BASE64_ENCODE_MULTILINE);
+  if (n < 0)
+    return -1;
+  offset += n;
+  if (BUG(offset > destlen))
+    return -1;
+
+  if (tor_snprintf(dest + offset, destlen - offset,
+                   "-----END %s-----\n", objtype) < 0)
+    return -1;
+
+  tor_assert(strlen(dest) + 1 <= pem_encoded_size(srclen, objtype));
+  return 0;
+}
+
+/**
+ * Given a PEM-encoded block of size <b>srclen</b> in <b>src</b>, if it has
+ * object type <b>objtype</b>, decode it into the <b>destlen</b>-byte buffer
+ * at <b>dest</b>.  Return the number of characters decoded on success, or -1
+ * on failure.
+ */
+int
+pem_decode(uint8_t *dest, size_t destlen, const char *src, size_t srclen,
+           const char *objtype)
+{
+  const char *eos = src + srclen;
+
+  src = eat_whitespace_eos(src, eos);
+
+  char *tag = NULL;
+  tor_asprintf(&tag, "-----BEGIN %s-----\n", objtype);
+  if ((size_t)(eos-src) < strlen(tag) || fast_memneq(src, tag, strlen(tag))) {
+    tor_free(tag);
+    return -1;
+  }
+  src += strlen(tag);
+  tor_free(tag);
+
+  // NOTE lack of trailing \n.  We do not enforce its presence.
+  tor_asprintf(&tag, "\n-----END %s-----", objtype);
+  const char *end_of_base64 = tor_memstr(src, eos-src, tag);
+  tor_free(tag);
+  if (end_of_base64 == NULL)
+    return -1;
+
+  /* Should we actually allow extra stuff at the end? */
+
+  return base64_decode((char*)dest, destlen, src, end_of_base64-src);
+}

src/lib/encoding/pem.h

@@ -0,0 +1,26 @@
+/* Copyright (c) 2001, Matej Pfajfar.
+ * Copyright (c) 2001-2004, Roger Dingledine.
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file pem.h
+ *
+ * \brief Header for pem.c
+ **/
+
+#ifndef TOR_PEM_H
+#define TOR_PEM_H
+
+#include "orconfig.h"
+#include <stddef.h>
+#include "lib/cc/torint.h"
+
+size_t pem_encoded_size(size_t src_len, const char *objtype);
+int pem_encode(char *dest, size_t destlen, const uint8_t *src, size_t srclen,
+               const char *objtype);
+int pem_decode(uint8_t *dest, size_t destlen, const char *src, size_t srclen,
+               const char *objtype);
+
+#endif