Formatting keys for import

This topic describes how to format your keys so that they can be imported by Cloud KMS as new key versions.

The correct format for your key material varies based on whether the key material is being imported into a symmetric key, or into an asymmetric key. For more information about the difference between symmetric and asymmetric keys, see Key purposes and algorithms.

Supported key formats

  • Symmetric keys for encryption: Imported symmetric keys must be 16 bytes (for raw symmetric encryption only) or 32 bytes of binary data, and must not be encoded. If your key is hex-encoded or base64-encoded, then you must decode it before attempting to import it.
  • Symmetric keys for signing (MAC keys): Imported HMAC signing keys must have a length equal to the output length of the cryptographic hash function being used (for example, HMAC-SHA256 keys must have a length of 32 bytes), and must not be encoded. If your key is hex-encoded or base64-encoded, then you must decode it before attempting to import it.
  • Asymmetric keys for encryption or signing: Imported asymmetric keys must be in PKCS #8 format and must be DER-encoded. PCKS #8 format is defined in RFC 5208. DER encoding is defined in International Telecommunications Union X.680. Asymmetric keys must use one of the length and algorithm combinations supported by Cloud KMS.

Some aspects of a key, such as the key's length, cannot be changed after the key is created. In these cases, the key cannot be imported into Cloud KMS.

Checking a symmetric key

Use the wc command to check a symmetric key's length.

wc -c /path/to/unwrapped-key

  • You cannot import a symmetric encryption key with a length other than 32.

  • Symmetric signing keys (MAC keys) must have a length equal to the output length of the cryptographic hash function being used (e.g. HMAC-SHA256 keys must have a length of 32 bytes).

Use the file command to check a key's format.

file /path/to/unwrapped-key

  • If the output is data, the key is in the correct format to be imported.

  • If the output is ASCII text, use the cat command to display the contents of the file.

    • If it is a string of letters and numbers ending in an = sign, it might be base64-encoded. Use the base64 command (Base64.exe on Windows) to decode it. The following is an example of a base64-encoded key:

      THzArjassB+giKeNeT1Zr74OgV24t+Ep+37Ec6ojB3Y=

    • If it contains one or more lines of hexadecimal numbers, it might be hex-encoded. Use the xxd command (or the Format-Hex PowerShell command on Windows) to decode it. The following is an example of a hex-encoded key:

      00000000: 4c7c c0ae 36ac b01f a088 a78d 793d 59af  L|..6.......y=Y.
00000010: be0e 815d b8b7 e129 fb7e c473 aa23 0776  ...]...).~.s.#.v

    • If it contains any other text, it may not be a valid symmetric key.