1. A concealing apparatus comprising: one or more hardware processors configured to: generate a concealed text by concealing a plaintext with a concealing key; generate mapping information that is mapped to a keyword such that different mapping information is associated with each instance of the same keyword; generate a tag based on the keyword and the mapping information; and output the concealed text and the tag as a pair to external storage storing a plurality of concealed texts each of which is paired with a tag, wherein the tag is transmitted to the external storage when retrieving the concealed text.
1. A concealing apparatus comprising: one or more hardware processors configured to: generate a concealed text by concealing a plaintext with a concealing key; generate mapping information that is mapped to a keyword such that different mapping information is associated with each instance of the same keyword; generate a tag based on the keyword and the mapping information; and output the concealed text and the tag as a pair to external storage storing a plurality of concealed texts each of which is paired with a tag, wherein the tag is transmitted to the external storage when retrieving the concealed text. 10. The apparatus according to claim 1 , wherein the one or more hardware processors generates the concealed text by encrypting the plaintext with the concealing key.