While it was printed about 11 years ago, I just got around to reading The Design of Rijndael: AES - The Advanced Encryption Standard. Appropois given that the RSA conference is next week.
Many information security titles over a decade old are obsolete (such as those on Windows NT and OS/2 security), but the Rijndael algorithm which became the AES (Advanced Encryption Standard) is still very much relevant.
Written by Joan Daemen and Vincent Rijmen, creators of Rijndael; the book presents a unique perspective.
The book is about the design and architecture of the algorithm. The authors note that the book was written for two kinds of readers. The largest group of readers will be those who want to read a full and unambiguous decryption of Rijndael. A large part of the book is aimed at the reader who wants to know why the authors created Rijndael and the way in which they did it.
The book is written for those that have a strong background with the mathematics of cryptography. Understanding the mathematics is not necessary for a full and correct understanding of Rijndael, but it is necessary for a good understanding of their design motivations.
For those that want a first-hand understanding of Rijndael, The Design of Rijndael: AES - The Advanced Encryption Standard is the book.