digest: add OpenSSL::Digest#squeeze#1083
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vcsjones
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Jul 8, 2026
| GetDigest(self, ctx); | ||
| str = rb_str_new(NULL, EVP_MD_CTX_size(ctx)); | ||
| int size = EVP_MD_CTX_size(ctx); | ||
| if (size < 0) { |
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In OpenSSL 1.1.1, EVP_MD_CTX_size actually return positive values and SHAKE128 and SHAKE256 actually "work". OpenSSL 3.0 broke this intentionally because it was kind of wrong to return anything, and what OpenSSL 1.1.1 returned was actually even more wrong.
Perhaps this is the behavior you want and SHAKE128 working in OpenSSL 1.1.1 is fine using just #digest.
With OpenSSL 1.1.1
EVP_shake128() -> 16
EVP_shake256() -> 32
The reason why this is "bad" is because SHAKE256 should actually return a 512-bit value for 256-bits of security, and SHAKE128 should return 256.
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It seems this was changed in OpenSSL 3.4. The old defaults don't seem right, but it's probably not ruby/openssl's job to fix it.
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Add support for extendable-output functions (XOFs). An XOF is a hash function that can produce arbitrary length of output. The interface of the existing Digest::Class#digest and its variants is unsuitable for this purpose. Add a new method to "squeeze" the specified amount of output from the XOF. This method can be called repeatedly. OpenSSL 3.3 or later and AWS-LC support this.
In OpenSSL 3.4 or later, SHAKE digests do not have a default output length and EVP_MD_CTX_size() returns -1. Raise OpenSSL::Digest::DigestError if the function returns a negative number. Fortunately, this is currently caught by a sanity check in rb_str_new() and leads to ArgumentError with the message "negative string size (or size too big)". Still, the caller should check it. Also, override #inspect to rescue an exception raised in #hexdigest.
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Closes #1082