問一個密碼學解密問題

這問題是出自一本偵探小說，作者是桃樂絲•賽兒絲(Dorothy L. Sayers)，問題如下：

In one of Dorothy Sayers's mysteries, Lord Peter is confronted with
the message shown in following figure 1. He also discovers the key to the message, which is a sequence of integers:

787656543432112343456567878878765654
3432112343456567878878765654433211234

Decrypt the message. Hint: what is the largest integer value?

I thought to see fairies in the fields, but I saw only the evil
elephants with their black backs. Woe! how that sight awed me! The
elves danced all around andabout while I heard voices calling clearly.
Ah! how I tried to see-throw off the ugly cloud-but no blind eye of a
mortal was permitted to spy them. so then came minstrels, having gold
trumpets, harps and drums. These played very loudly beside me,
breaking that spell. So the dream vanished, whereat I thanked Heaven. I
shed many tears before the thin moon rose up, frail and faint as a sickle of
straw. Now though the Enchanter gnash his teeth vainly, yet shall he
return as the spring returns. Oh, wretched man! Hell gapes, Erebus now
lies open. the months of Death wait on thy end.

它說關鍵在於最大的整數，我搜尋其他網頁後知道最大值，但我看不出來這值跟那些數字與文章有任何關係，有人知道其中的奧秘嗎