Boomers basically promised themselves that younger taxpayers would pay them a bunch of money in retirement, and then they didn’t go and make the taxpayers. 
Not true, not at all. The boomers are scheduled to receive in benefits only about the exact amount they paid in through taxes.  The last time I looked at the SSA actuarial data the “break even” cohort was birth year 1953 (hey, that’s me!) right in the middle of the boomer birth years.
The problem is the pre-boomer generation received hugely more in benefits than they paid in. The first SS beneficiary to receive a check, Ida May Fuller, paid total taxes of $24.75 and received $22,888.92 in benefits.
The boomers’ taxes were used to pay the benefits of Ida and her pre-boomer compatriots. Now, who’s going to pay for the boomers (me!!)?   The Nobelist Paul Samuelson said not to worry because “Social Security is a Ponzi Scheme That Works“….

The beauty of social insurance is that it is actuarially unsound. Everyone who reaches retirement age is given benefit privileges that far exceed anything he has paid in — exceed his payments by more than ten times (or five times counting employer payments)!How is it possible? It stems from the fact that the national product is growing at a compound interest rate and can be expected to do so for as far ahead as the eye cannot see. Always there are more youths than old folks in a growing population.More important, with real income going up at 3% per year, the taxable base on which benefits rest is always much greater than the taxes paid historically by the generation now retired.Social Security is squarely based on what has been called the eight wonder of the world — compound interest. A growing nation is the greatest Ponzi game ever contrived.
 — writing in Newsweek, 1967

That is, social insurance being actuarially unsound was a feature, not a bug — not just for Social Security but also for then-young Medicare.  If Paul was still around, he might want that one back.  
Interestingly, FDR had a much better handle on this than the great economist.  When his SS Act of 1935 passed he proclaimed it “actuarially sound and out of the Treasury forever”, and meant it.  It wasn’t going to pay full benefits for a couple decades and then they would be based on the interest rate earned on the federal bonds that workers’ payroll taxes had bought to fund them.  He was absolutely insistent that no general revenue ever be called into the system.  When he discovered that 30 years later, in the 1960s (!!), his draft program called for some general revenue to top off benefits, he had a famous tantrum and ordered the bill withdrawn from Congress and re-written.  Yes, FDR, the creator of the New Deal, was fiscally far more conservative than anyone in politics today.  Ponder.
His program lasted all the way until the payroll taxes started coming in.  Then, incentives! free cash!! political incentives!!!  The Left decried all that tax revenue going into bonds and demanded that it be spent on, er, invested in, their favorite social projects instead (in the 1930s they had quite a list).  The Right said, we can’t let the left squander the money like that, and the tax rate is too high, tax cuts for workers!  They compromised by increasing and expanding benefits while cutting the payroll tax rate in half. 
Arthur Altmeyer, FDR’s head of SS, objected to Congress that by arithmetic this would make SS insolvent in the long run (see 1983), and that giving Ida & Co benefits so much higher than the bond rate would force future benefits to be below the bond rate (see today, and getting worse) which would be unfair to future workers and cripple SS’s future credibility with them. He reported that the Congressional leaders replied, “That will be somebody else’s problem”.  Ida voted then!  
FDR vetoed Congress’s enactment of the changes. Congress over-rode his veto.  It was his only veto ever to be over-ridden.  Such is the power of political incentives over fiscal planning.  That’s not going to change now.
The details of the story are really educational about politics.  The SSA has an excellent history section on its web site, and my favorite book on it all is “The Real Deal” by Schieber & Shoven.  It’s out of print now but Schieber was past chairman of the Social Security Advisory Board and is authoritative.   It dates back to when politics was sane enough to be bitterly loopy about important issues (“SS reformers want to make grandma eat cat food”) instead of about who uses what bathroom, and covers all the bases.

So the only possible options are taxes go up and/or benefits go down. 
Is that your definition of a “credible” solution?
None of the two is “credible”.
If we go for non-credible solutions, putting behind bars all the politicians responsible for this Ponzi scheme would be a much better one (after all, that’s what we do with the people running this kind of schemes).