cryptlib is distributed under a dual license that allows free, open-source use under a GPL-compatible license (a.k.a. the Sleepycat License) and closed-source use under a standard commercial license.  In addition, cryptlib is free for use in low-cost, non-open-source applications such as shareware, and for personal and academic or research use.
All commercial users must obtain a commercial license, which will be negotiated and agreed with Digital Data Security Limited, the registered owner of the cryptlib software. Specifically, any large-scale commercial use of cryptlib requires a license. "Large-scale commercial use" means any revenue-generating purpose such as use for company-internal purposes, or use of cryptlib in an application or product, with a total gross revenue of over US$5,000.  This allows cryptlib to be used in freeware and shareware applications, for evaluation and research purposes, and for non-revenue-generating or personal use without charge.  In addition the author reserves the right to grant free licenses for commercial use in special cases (for example where there is a general benefit to the public), however you must contact the author for permission if you think you qualify.