Don’t Use PGP For Cloud Storage!
Exceptions exist. This is a general guide for non-cryptographers.
One would disagree. Whilst PGP provides currently ample protection against conventional cryptographic attacks*, PGP’s key encapsulation mechanism (KEM) is weak against post quantum (PQ) attacks.
Furthermore, asymmetric cryptography would appear inappropriate for this type of cloud storage (whereby the user encrypts-then-uploads; and downloads-then-decrypts). In this scenario the user holds the private key and is only encrypting to one’s own public key, hence asymmetric cryptography is providing no security benefit, but rather a security weakness, as previously evidenced vis-a-vis KEM.
On the other-hand, symmetric cryptography, such as AES and ChaCha20, are not currently affected by PQ attacks**. Furthermore, the key deviation functions (KDF) are not vulnerable to any quantum attacks***. In synthesis, a purely symmetric scheme, e.g. AES-256-GCM-Argon2, would provide substantially greater protection against both conventional and PQ attacks, compared to asymmetric cryptography, especially RSA.
*assuming a sufficiently secure key (e.g. Curve25519).
**according to the current literature.
***assuming the KDF does not use any asymmetric schemes, which most do not.
PGP/GPG can be configured to use either RSA or ECC along with AES within a hybrid encryption scheme.
Hybrid encryption schemes use both symmetric and asymmetric cryptography; however, the asymmetric cryptography is vulnerable due to the KEM, not the encryption cipher.
Use symmetric cryptographic schemes, in this instance, as it providers greater protection against both conventional and post-quantum attacks.
A example of symmetric cryptography would be AES-256-GCM-Argon2, where “AES” is the cipher, “256” is the key length, “GCM” is the cipher mode (please choose the cipher-mode carefully), and “Argon2” is the KDF (the algorithm which turns your password into a key).
Alternatively, use XChaCha20Polly1305 with Argon2.
If Argon2 is unavailable use: scrypt, bcrypt or PBKDF2.