Encryption result with iPhone 14 devices

Hi

I have code that uses SecKeyEncrypt to encrypt a string.

SecKeyEncrypt(publickeysi!, SecPadding.PKCS1, aString, aString.count, &messageEncrypted, &messageEncryptedSize)

This works across all devices, given identical source string, except the recently released iPhone 14 and Pro models. Simulator works across the board.

Is there any reason why these devices would result in a B64 encoded string along the lines of

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==

where all other devices return an appropriate B64 string, such as

DNfdGmJW8DOeuwB9DZxMjY/qcJHgKCewMd/Hi3m1vkHxdRaeQbYvFbmnJwtcudnqm9cRiT/cee1ls5Hm6bcmVtGPf23O4SnOha97MhrJIaUWOumUdRfKd5PYVd74NVuWPfQ+VHlKFQtiVjBNvNntiZmadBEV95BwRcxFWSVLDG7tfgzM2tNvYsDG+ZwN0r3F1AX4IH/Ggor9Dk//26c5WZ50HzwfkeY122qMDIj2LDCUGXXhXzkvSyEYFReJhscwtXdDk1nN49jrDB5bEUD9Xn1xZzlghpcSNC4DKqP/3TSuwqcHZ7g/BfYcRVtXeWGqUxeeQcaTNulUggCWWGdtJw==

It appears that SecKeyEncrypt is deprecated in iOS 15 but I am struggling to find an appropriate alternative if that is even the issue.

Thanks