The Secure Hash Algorithm (SHA) is a one-way message digest algorithm. There are actually two different forms of the Secure Hash Algorithm:
SHA-1 is defined in RFC 3174 and generates a 160-bit digest.
SHA-2 is defined in RFC 4634 and can be used to generate 256-bit, 384-bit, or 512-bit digests.
All forms of the Secure Hash Algorithm are considered stronger than the MD5 algorithm. There have been recent advancements that may indicate a weakening of the SHA-1 variant, but nevertheless there is no evidence to suggest that the way it is used in the directory server is under any danger, nor is there any concern about any of the SHA-2 encodings.