Acidic conditions, high heat, and return to carboxylic acids
In the cyanohydrin reaction aldehydes or ketones can react with HCN to form a cyanohydrin.  Inorganic cynanides and acid can be used in place of HCN, to generate the required cyanide anion.   The reaction proceeds by typical addition of the nucleophilic cyanide anion to the carbonyl carbon to form the tetrahedral intermediate, which can ultimately be protonated to yield the corresponding cyanohydrin.



Once formed, the nitrile group of the cyanohydrin can undergo acidic (or basic) hydrolysis by the same mechanism as any other common nitrile.  The only difference in the case of a cyanohydrin is that the "R" group contains a hydroxyl substituent on its alpha carbon.



A useful variant of cyanohydrin formation is the Strecker amino acid synthesis.  Instead of forming a cyanohydrin, an aminonitrile is formed and the nitrile is hydrolyzed to the corresponding alpha-amino acid.  A detailed mechanism can be found in the above link.