The issue is twofold: decoding a DER input with sequences and locating
a specific element in a sequence. Even though a DER sequence is
conceptually an array, in libtasn1 it is represented as a linked list,
whose elements are assigned a string name, such as "?1". Therefore a
simple lookup of an element at a given position is linear O(N) time
complexity. When decoding a DER sequence, in each step libtasn1 looks
up the parent node, recorded on the first element, which requires a
backward linear search, resulting in O(N^2) time complexity.