וַיִּקְרָא פַרְעֹה שֵׁם יוֹסֵף צָפְנַת פַּעְנֵחַ
And Pharaoh named Joseph "Tzafnas Pa'neach" [Miketz 41:45]
Rashi explains: "Tzafnas Pa'neach - mepharesh hatzefunos [decipherer of the cryptic]"
If that is the meaning of Yosef's title, asked the Sefas Emes [R' Yehudah Leib Alter of Gur], then would it not have been more appropriate to reverse the order of the words and refer to him as "Paneach tzefunos"?
Yosef, answered the Sefas Emes, merited his unique ability to reveal that which was concealed on account of the fact that he acted with extreme modesty, always concealing his own righteousness from the eyes of others.
It is for this reason, he concluded, that he was referred to as Tzafnas Pa'neach. Tzafnas - because he went to great lengths to hide his greatness ["tzafnas" - the hidden one], "paneach" - he merited to decipher hidden matters.
Source: Rabbi Yisrael Bronstein