How to split a PEM file

Solution 1:

The awk snippet works for extracting the different parts, but you still need to know which section is the key / cert / chain. I needed to extract a specific section, and found this on the OpenSSL mailinglist: http://openssl.6102.n7.nabble.com/Convert-pem-to-crt-and-key-files-tp47681p47697.html

# Extract key
openssl pkey -in foo.pem -out foo-key.pem

# Extract all the certs
openssl crl2pkcs7 -nocrl -certfile foo.pem |
  openssl pkcs7 -print_certs -out foo-certs.pem

# Extract the textually first cert as DER
openssl x509 -in foo.pem -outform DER -out first-cert.der

Solution 2:

The split command is available on most systems, and its invocation is likely easier to remember.

If you have a file collection.pem that you want to split into individual-* files, use:

split -p "-----BEGIN CERTIFICATE-----" collection.pem individual-

If you don't have split, you could try csplit:

csplit -s -z -f individual- collection.pem '/-----BEGIN CERTIFICATE-----/' '{*}'

-s skips printing output of file sizes

-z does not create empty files

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Solution 3:

This was previously answered on StackOverflow :

awk '
  split_after == 1 {n++;split_after=0}
  /-----END CERTIFICATE-----/ {split_after=1}
  {print > "cert" n ".pem"}' < $file

Edit 29/03/2016 : See @slugchewer answer

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Solution 4:

If you want to get a single certificate out of a multi-certificate PEM bundle, try:

$ openssl crl2pkcs7 -nocrl -certfile INPUT.PEM | \
    openssl pkcs7 -print_certs | \
    awk '/subject.*CN=host.domain.com/,/END CERTIFICATE/'

• The first two openssl commands will process a PEM file and and spit it back out with pre-pended "subject:" and "issuer:" lines before each cert. If your PEM is already formatted this way, all you need is the final awk command.
• The awk command will spit out the individual PEM matching the CN (common name) string.

source1 , source2

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Solution 5:

If you are handling full chain certificates (i.e. the ones generated by letsencrypt / certbot etc), which are a concatenation of the certificate and the certificate authority chain, you can use bash string manipulation.

For example:

# content of /path/to/fullchain.pem
-----BEGIN CERTIFICATE-----
some long base64 string containing
the certificate
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE-----
another base64 string
containing the first certificate
in the authority chain
-----END CERTIFICATE-----

-----BEGIN CERTIFICATE-----
another base64 string
containing the second certificate
in the authority chain
(there might be more...)
-----END CERTIFICATE-----

To extract the certificate and the certificate authority chain into variables:

# load the certificate into a variable
FULLCHAIN=$(</path/to/fullchain.pem)
CERTIFICATE="${FULLCHAIN%%-----END CERTIFICATE-----*}-----END CERTIFICATE-----"
CHAIN=$(echo -e "${FULLCHAIN#*-----END CERTIFICATE-----}" | sed '/./,$!d')

Explanation:

Instead of using awk or openssl (which are powerful tools but not always available, i.e. in Docker Alpine images), you can use bash string manipulation.

"${FULLCHAIN%%-----END CERTIFICATE-----*}-----END CERTIFICATE-----": from end of the content of FULLCHAIN, return the longest substring match, then concat -----END CERTIFICATE----- as it get stripped away. The * matches all the characters after -----END CERTIFICATE-----.

$(echo -e "${FULLCHAIN#*-----END CERTIFICATE-----}" | sed '/./,$!d'): from the beginning of the content of FULLCHAIN, return the shortest substring match, then strip leading new lines. Likewise, the * matches all the characters before -----END CERTIFICATE-----.

For a quick reference (while you can find more about string manipulation in bash here):

${VAR#substring}= the shortest substring from the beginning of the content of VAR

${VAR%substring}= the shortest substring from the end of the content of VAR

${VAR##substring}= the longest substring from the beginning of the content of VAR

${VAR%%substring}= the longest substring from the end of the content of VAR