Shihō

Shihō (嗣法^?) refers to a series of ceremonies in Sōtō Zen Buddhism wherein a unsui receives Dharma transmission, becoming part of the dharma lineage of his or her teacher.

Shiho is done "one-to-one in the abbot's quarters (hojo)".

Shiho, or denpo, is the Dharma transmission ceremony where the student inherits the Dharma, and is empowered to transmit the lineage. In the denpo ceremony, the student becomes an ancestor of the tradition and receives a robe and bowl, among other objects.

During the denpo ceremony the student receives a Shoshike certificate, which grants the power to perform Jukai, and the documents known as the "three regalia of transmission":

a) Shisho (the scripture of transmission, the names of the anscestors arranged in a circle - the dharma has passed on from to Shakyamuni to yourself, and now you give it back to Shakyamuni. There is a small piece of paper, probably originally written by Sawaki Roshi, with some comments. This paper is also copied by the student when doing dharma transmission at Antaiji.)

b) Daiji (the great matter, a cryptic symbolization of the content of the teaching. Again, there is a small extra sheet of paper that explains about the meaning of the symbols.)
c) Kechimyaku (the blood lineage, looks quite similar to the blood line transmission that you already wrote at the time of ordination)
d) Actually, in the lineage of Sawaki Roshi (and maybe other lineages as well) a student is told to write a fourth document on an extra sheet of paper, which is called Hisho (the secret document, which is encoded, but the code for deciphering is on the same paper, so once you hold it in your hands it is not so "secret" anymore.)

The Sōtō-shu also confers inka shōmyō (or inshō) "[granting] the seal of approval to a realization of enlightenment", upon students. This is an

... idealized religious aspect of the Dharma transmission process. Zen master and disciple may evoke this mystical paradigm through ritual ceremony in the master's room (shi-tsunai), but other, more mundane institutional concerns can govern the actual selection and promotion of Dharma 'heirs'.

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Wikipedia