Cryptography Engineering is less advanced than Serious Cryptography (but it's "take-y-er"; there's a lot of opinion / best practices stuff in it, and a lot of that is good).
I'd say that if you've read and grokked Serious Cryptography, and you don't want to write code, something like _IMC_ (Silverman, above) is an interesting next step, in that you'll mostly be reasoning about math, and you'll be working at a much lower level than the basic RSA formulae.
It also depends on what aspects of cryptography are interesting to you. If you want, for instance, to get a much better grip on how bulk cryptography works, as opposed to signatures and key exchanges, your best next step might be papers. For instance, a good next step on block cipher cryptography would be the Heys tutorial: https://ioactive.com/wp-content/uploads/2015/07/ldc_tutorial...
I'd say that if you've read and grokked Serious Cryptography, and you don't want to write code, something like _IMC_ (Silverman, above) is an interesting next step, in that you'll mostly be reasoning about math, and you'll be working at a much lower level than the basic RSA formulae.
It also depends on what aspects of cryptography are interesting to you. If you want, for instance, to get a much better grip on how bulk cryptography works, as opposed to signatures and key exchanges, your best next step might be papers. For instance, a good next step on block cipher cryptography would be the Heys tutorial: https://ioactive.com/wp-content/uploads/2015/07/ldc_tutorial...