Baek et al. [34] presented a highly efficient ASA on the
digital signature algorithm (DSA) and implemented the proposed ASA by replacing the original DSA in Libgcrypt with
the subverted DSA. Due to multiple surveillants for different
governments or manufacturers, Li et al. [35] initializes the
analysis of security against subversion in a multi-surveillant
setting. They introduced a security notion that the transmission of a real message is undetectable, which means
all surveillants either think the users transmit an innocuous
message by the subverted algorithms, or consider users are
using non-subverted algorithms. Lv et al. [36] investigated
the study of subversion attacks against cloud auditing protocol. In addition, Schneier et al. [37] categorized a broader
set of potential avenues for the subversion of cryptographic
systems.
II. SYMMETRIC ENCRYPTION SCHEME AND ITS ASA

This section uses the formal method to describe the symmetric encryption scheme and its ASA. Next, two crucial
concepts, i.e., the correctness and the decryptability, are
respectively defined in the formal sense. The correctness denotes the error rate of the encryption and decryption process without considering the ASA. Comparatively,
the decryptability denotes the error rate of the encryption and
decryption process under the ASA.
A. SYMBOLS AND NOTATIONS

We follow the symbols and notations in [1], [2] to discuss the
symmetric encryption scheme and its subversion.
• {0, 1}n denotes the set of n-bit strings.
• {0, 1}∗ denotes the set of all strings.
• ⊥ denotes a special symbol standing for ‘‘invalid’’ or
‘‘reject’’.
• ε denotes the empty string.
• N denotes the set of the natural numbers.

### Language ###
English

### Assessment ###
Information about what the notation "⊥" means in technical/mathematical notation

### Query ###
Can someone explain what the symbol "⊥" represents in mathematical notation?

The query is legitimate as it seeks to understand a mathematical symbol, and someone could naturally ask this without knowing about this specific text. The answer is clearly present in the text which states it "denotes a special symbol standing for 'invalid' or 'reject'."
Can someone explain what the symbol "⊥" represents in mathematical notation?

The query is legitimate as it seeks to understand a mathematical symbol, and someone could naturally ask this without knowing about this specific text. The answer is clearly present in the text which states it "denotes a special symbol standing for 'invalid' or 'reject'."