The following is a plaintext key (no passphrase provided).

The new "v1" format contains the header "-----BEGIN OPENSSH PRIVATE KEY-----"
and the footer "-----END OPENSSH PRIVATE KEY-----".

All length ints are uint32, network-byte order.

PEM:
-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAMwAAAAtzc2gtZW
QyNTUxOQAAACBEOIvJc2hN1mhXExEiv/ISyYO7prFixOl80R9zw52XsAAAAJjPbUqwz21K
sAAAAAtzc2gtZWQyNTUxOQAAACBEOIvJc2hN1mhXExEiv/ISyYO7prFixOl80R9zw52XsA
AAAEBqSF+KwoLTOqI6+TnpcaZY4ckcamLrBF8CvtJbNZflJ0Q4i8lzaE3WaFcTESK/8hLJ
g7umsWLE6XzRH3PDnZewAAAAElRoaXMgaXMgYSB0ZXN0IGtleQECAw==
-----END OPENSSH PRIVATE KEY-----

HEX (only base64 string above):
00000000: 6f70 656e 7373 682d 6b65 792d 7631 0000  openssh-key-v1..
00000010: 0000 046e 6f6e 6500 0000 046e 6f6e 6500  ...none....none.
00000020: 0000 0000 0000 0100 0000 3300 0000 0b73  ..........3....s
00000030: 7368 2d65 6432 3535 3139 0000 0020 4438  sh-ed25519... D8
00000040: 8bc9 7368 4dd6 6857 1311 22bf f212 c983  ..shM.hW..".....
00000050: bba6 b162 c4e9 7cd1 1f73 c39d 97b0 0000  ...b..|..s......
00000060: 0098 cf6d 4ab0 cf6d 4ab0 0000 000b 7373  ...mJ..mJ.....ss
00000070: 682d 6564 3235 3531 3900 0000 2044 388b  h-ed25519... D8.
00000080: c973 684d d668 5713 1122 bff2 12c9 83bb  .shM.hW.."......
00000090: a6b1 62c4 e97c d11f 73c3 9d97 b000 0000  ..b..|..s.......
000000a0: 406a 485f 8ac2 82d3 3aa2 3af9 39e9 71a6  @jH_....:.:.9.q.
000000b0: 58e1 c91c 6a62 eb04 5f02 bed2 5b35 97e5  X...jb.._...[5..
000000c0: 2744 388b c973 684d d668 5713 1122 bff2  'D8..shM.hW.."..
000000d0: 12c9 83bb a6b1 62c4 e97c d11f 73c3 9d97  ......b..|..s...
000000e0: b000 0000 1254 6869 7320 6973 2061 2074  .....This is a t
000000f0: 6573 7420 6b65 7901 0203                 est key...

ANNOTATED HEX:
0 6f70656e7373682d6b65792d763100 ("openssh-key-v1" + 0x00)
1.0 00000004 (4)
	1.0.0 6e6f6e65 ("none")
2.0 00000004 (4)
	2.0.0 6e6f6e65 ("none")
3.0 00000000 (0x00)
	3.0.0 (N/A)
4.0 00000001 (1)
	4.0.0 00000033 (51)
		4.0.0.0 0000000b (11)
			4.0.0.0.0 7373682d65643235353139 ("ssh-ed25519")
		4.0.0.1 00000020 (32)
			4.0.0.1.0 44388bc973684dd66857131122bff212c983bba6b162c4e97cd11f73c39d97b0 (bytes)
	4.0.1 00000098 (151)
		4.0.1.0 cf6d4ab0 (3480046256)
		4.0.1.1 cf6d4ab0 (3480046256)
		4.0.1.2 -
			4.0.1.2.0 0000000b (11)
				4.0.1.2.0.0 7373682d65643235353139 ("ssh-ed25519")
			4.0.1.2.1 00000020 (32)
				4.0.1.2.1.0 44388bc973684dd66857131122bff212c983bba6b162c4e97cd11f73c39d97b0 (bytes)
		4.0.1.3 00000040 (64)
			4.0.1.3.0 6a485f8ac282d33aa23af939e971a658e1c91c6a62eb045f02bed25b3597e527
					  44388bc973684dd66857131122bff212c983bba6b162c4e97cd11f73c39d97b0 (bytes)
		4.0.1.4 00000012 (18)
			4.0.1.4.0 5468697320697320612074657374206b6579 ("This is a test key")
		4.0.1.5 010203 ([1 2 3], 3 bytes)