Add asserts to help out Coverity

It somehow deduces an input that is both > 0 and for which high_bit
never finds a bit set and returns 0. In both cases that would lead to
block being 0 and a negative shift.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/lib/asn1/der_enc.cpp b/src/lib/asn1/der_enc.cpp
index 871171153..c5c2b4803 100644
--- a/src/lib/asn1/der_enc.cpp
+++ b/src/lib/asn1/der_enc.cpp
@@ -34,6 +34,8 @@ secure_vector<byte> encode_tag(ASN1_Tag type_tag, ASN1_Tag class_tag)
       size_t blocks = high_bit(type_tag) + 6;
       blocks = (blocks - (blocks % 7)) / 7;
 
+      BOTAN_ASSERT(blocks > 0, "Math works");
+
       encoded_tag.push_back(class_tag | 0x1F);
       for(size_t i = 0; i != blocks - 1; ++i)
          encoded_tag.push_back(0x80 | ((type_tag >> 7*(blocks-i-1)) & 0x7F));