1 files changed, 25 insertions, 0 deletions
diff --git a/src/sbearssl/sbearssl_isder.c b/src/sbearssl/sbearssl_isder.c
new file mode 100644
index 0000000..c481da9
--- /dev/null
+++ b/src/sbearssl/sbearssl_isder.c
@@ -0,0 +1,25 @@
+/* ISC license. */
+
+#include <sys/types.h>
+#include <s6-networking/sbearssl.h>
+
+int sbearssl_isder (unsigned char const *s, size_t len)
+{
+  size_t dlen = 0 ;
+  unsigned char c ;
+
+  if (len < 2) return 0 ;
+  if (*s++ != 0x30) return 0 ;
+  c = *s++ ; len -= 2;
+  if (c < 0x80) return (size_t)c == len ;
+  else if (c == 0x80) return 0 ;
+  c -= 0x80 ;
+  if (len < (size_t)c + 2) return 0 ;
+  len -= (size_t)c ;
+  while (c--)
+  {
+    if (dlen > (len >> 8)) return 0 ;
+    dlen = (dlen << 8) + (size_t)*s++ ;
+  }
+  return dlen == len ;
+}